Actually Hudson was probably 39 at the time of filming. On the Criterion DVD, one of the special features includes a still of a scene being shot with a date of 6/21/1965. Hudson''s DOB was 11/17/1925. I'd say he looks "40ish", not particularly youthful with somewhat haggard features.
The film depicts a full body ""makeover", that is the Arthur Hamilton body is transformed into something much bigger, stronger and more muscular. However, they don't indicate that vital internal organs have been replaced.

wow the B&W must've made him look older especially the beginning where his hair was white. man's favorite game was around the same time and he looked much younger in color than in seconds.

Rock Hudson was actually forty when the movie was made.

Rock looked a lot older than 30-35 to me. I would say he looked early 50s (a very handsome man of that age, but still of that age). dying the hair alone made him look significantly younger (say 50 instead of 55).

Rock Hudson was 41 not 30-35 when this movie was made.
Yes, the banker looked a little younger afterwards, but with the surgery & physical conditioning, I think it was within possibilities.

"But the plot point that always irks me is that this is someone whose youth is gone for good. He's old, out-of-shape, and it's going to be downhill and shady all the way, healthwise. But Arthur Hamilton goes from looking like John Randolph (with all due respect), who looks way older than the average 50-year-old today (I'm 46 and people think I'm in my mid- to late-thirties), a saggy, old, not very goodlooking man who's reborn looking likeROCK HUDSON. And this is before Hudson started losing his looks to excessive boozing. Frankly, I don't see the problem. No offense, but if that were me, I'd be boffing everything in sight."
According to Frankenheimer on the commentary, the original concept called for the leads to be played by the same person. They landed Rock Hudson, but he stipulated he would only play the "after", so they cast Murray Hamilton as the "before". They then went to extra lengths to make the transformation as "believable" as possible. This is a plot hole of sorts, but remember he first requested "tennis pro" as his new life, and the company nixed that idea for his second choice of "artist". I think that was their way of telling us the new identity for Charlie Evans as Tony Wilson is little more than a facade, given his age and health problems, and to fill-in this "plot hole" and make it believable.
Overall it worked for me because of the way things worked out, but at the time of the "transformation" I was skeptical. And perhaps the reason why Tony Wilson didn't start boffing everything in site was because he just didn't have the libido of the younger man he was supposed to be?

I Agree with Mobocracy
The old guy that seems to lead the whole thing is wacky and could be super rich. He talks about giving people a new life almost as he wishes he could do it too but missed his chance and is spend all his money to play God.
But this movie doesn't work in our time because they had a different sense of paranoia then. Secret societies, super secret experiments, medical science for the sake of discover and not profit. Its all crazy thinking by today's logic. As for the money issue, they said he had to pay $30K, which is equal to about $250K now, but don't forget they probably have some great life insurance policies on these guys and are getting pay outs from the seconds deaths.

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'This makes even more sense as a possible intent given it was the era of "The Manchurian Candidate", "The Prisoner", brainwashing, and the CIA mind control-progam MK-ULTRA."'
it should probably also be noted that this is the 3rd film in frankenheimer's 'paranoia trilogy'. supports your idea.

I agree with the comment that this movie doesn't stand for two much specific scrutiny a la some of the questions raised. And it doesn't need to (although it is human nature to want to understand "all the details".) It's beauty is that it is a very "impressionistic" as well as imaginative (and dark) movie; and it explores a more fundamental concept.
Plus, it should be noted that, as someone once said, there are only about seven original stories; and that this movie, as is true of many others, is the retelling of a classic story. This movie is the "Faust" story.

I think accepting the notion that it is at least partially a science fiction film goes along way towards improving the verisimilitude of the narrative, at least from a biomedical perspective.
The motivations of "the company" are opaque enough that we might not even have to presume that these transformations are done on a for-profit, customer focused, revenue generating basis.
It very easily could be the weird pursuit of a single, wealthy individual (think Howard Hughes), or most likely, a government, pursuing some kind of covert intelligence research or operation. This makes even more sense as a possible intent given it was the era of "The Manchurian Candidate", "The Prisoner", brainwashing, and the CIA mind control-progam MK-ULTRA.

Actor John Randolph was 50 or 51 when this movie was filmed and released.
I agree that these are all valid questions. Here are some more. Obviously, the character was well-off. He lived in Scarsdale, so he qualified as affluent. Yet when you take into consideration all that went into making him a reborn, it makes one wonder whether the character's life insurance policy and "annuities," stocks, etc. would be enough to cover all the expense (although Will Geer does admit at the end that the operation isn't in profit yet).
Of course, we know that the "Cadaver Procurement Unit" is that large room with all those reborns waiting around for another "match" and a second chance at reborn status. In fact, the "mistakes," as Geer calls them, are "recycled," if you will, to make it appear that new candidates have diedthereby destroying their old identities. But just think of all the effort that has to go into that. Bodies are identified by their teeth, fingerprints, distinguishing marks (this was in the days before DNA analysis), but you could also add blood type.
How is all this "faked" to make it appear that John Randolph has died and been reborn as Rock Hudson?
And his widow is left comfortably off, as well, so all the money is not taken by the reborn company. Plus, the cost of surgery. Look at that hospital staff. And does all this remain a secret with so many involved?
An entirely new identity is created for Arthur Hamilton. He's an artist who has already had one-man shows. Nothing too newsworthy, mind you, but we see clippings that supposedly covered gallery shows that never happened but have been made to appear as if they have happened and this individual already pre-exists. Even Hudson is stunned that he's expected to assume such a full-fledged identity.
Then there's the house in Malibu. With a full-time man servant. And, a company assigned girlfriend (although she's clearly not his friendbut then she has her own interests to consider). All this for a man without a job.
And there's enough money to go around to cover all of this based on the aforementioned life insurance policy, annuities, stocks, etc. Wow, he must have had quite a bundle. It's a wonder he didn't have a "family compound" a la Hyannisport.
But the plot point that always irks me is that this is someone whose youth is gone for good. He's old, out-of-shape, and it's going to be downhill and shady all the way, healthwise. But Arthur Hamilton goes from looking like John Randolph (with all due respect), who looks way older than the average 50-year-old today (I'm 46 and people think I'm in my mid- to late-thirties), a saggy, old, not very goodlooking man who's reborn looking likeROCK HUDSON. And this is before Hudson started losing his looks to excessive boozing. Frankly, I don't see the problem. No offense, but if that were me, I'd be boffing everything in sight.
But this isn't a movie that holds up to such close scrutiny. We have to remember that "Seconds," although it doesn't appear to be on its surface, is a work of science fiction. It's not a movie about "what is" but about "what if?," and focuses on the individual's "adjustment problems," the nature of identity, and so on. Finally, it's a one-of-kind movie that is strangely haunting and troubling. A true gem.

I thought that the pills he was taking were tranquilizers or some other mood-modifying pill. I think circa early 60s, prescriptions for uppers, downers, laughers & screamers (to borrow a phrase from Hunter S. Thompson) were really quite commonplace, and it fits in with "the company" and its high-tech medical treatment.
I don't think it specifically spelled out some pre-existing medical condition that Arthur Hamilton had, just a generic reference to some kind of mother's little helper.

i think he was probably in his early 50s in the beginning. i see your point, and i think it's underlined by two subtle scenes:

1. before the transformation, arthur is sitting on the bed the night after charlie's second call and he's sweating and his wife asks him if he's feeling ok and his reply it: "yeah, it's just old faithful".
2. on the plane ride just after the transformation, just after the stewardess stops by he suddenly lunges to the bathroom and takes a pill of some sort.
   to me this underlined that he had a heart condition, and it wasn't fixed by his younger appearance. the fact that he was able to not "move like a senior citizen" was probably partially physical training (some was shown just after surgery) and the ability of the human mind to be fooled into believing what it sees.
   there are numerous studies on people who receive plastic surgery that they regain a "youthful" energy, the old "feel young, be young" phenomenon. it can even extend a person's lifespan; after all, so much of our health depends on our mental state. stress and depression have a tremendous effect on our physical health.
   it's another reason this movie is so brilliant. i just saw it for the first time. i kept having to check the jacket and imdb to make sure it was really made in 1966.
   i'm going to have to check out the novel.