I personally don't think she looked older than her years until about 1957 or so.
She looks her age, about thirty, in her wedding photos with Sinatra, in my judgment.

I'm afraid this was not the photo to use to show Ava's wear and tear. She looks lovely, and anywhere from 35 to maybe 40. In those days, women of 38 tended to look 38. The extremely sophisticated procedures used now on girls of 20, before they have even begun to mature, were unknown.
Personally, I like older Ava. With that bone structure she never quite (to me) lost her beauty, despite her bad habits.

https://twitter.com/4EvCarolinaGirl/status/772924222544941057
Ava Gardner is only 38 here but appears much older, due to her heavy drinking & smoking. #TCMParty #TheAngelWoreRed

I would rather have Ava Gardner look mature for her age than 40 year old Reese Witherspoon who who looks 34 but still acts like she's 25.

Hard drinking. Hard partying. It'll kill your looks. Poor Ava lost hers early. In her defense though, people did look older back then even when they were I their early 20's.
Actors are useless without the power of a good writer's imagination

If you'll notice, she's very thin at the time of her wedding to Sinatra, as is Frank, himself. They were both under a great deal of pressure from the time their relationship became public, through the divorce, and then the wedding. They both liked to drink, smoke and stay out all night. I think many actresses of that time looked more mature than do the ones of today, as people of that era were, in general, more mature because they had to be (Great Depression, WWII, etc.)
"No, I don't like to cook, but I have a chicken in the icebox, and you're eating it."

Smoking and alcohol could age terribly. Since late 1950s she used look seriously bloated as in movies as in photos. I think breadth and strength of her face must have an influence along with smoking and alcohol. That sort of face could aged women.
I agree she looks like a 'very beautiful and well-preserved 40' at her wedding to Sinatra.
https://67.media.tumblr.com/998541a457c0f8a38b9c12f134803f98/tumblr_nmgdkyGJSb1ql4a37o1_500.gif
https://67.media.tumblr.com/665fc7c0b724ea0ff483fbba08432009/tumblr_o82lbnBkMm1rzbj5mo1_250.gif
I saw others videos of them together during their marriage, she looks like she was in her late 30s. She looks like a beautiful striking looking (but not the most) woman aged 35, if not more. She looked better in movies than in videos I saw.

She was in Knots Landing 5 years before she died. And looked how you would expect a woman of that age to look. She didn't look particularly old for her age then. She was a heavy smoker though.