I wondered the same thing. He sure doesn't look 35!
~For beautiful eyes look for the good in others, for beautiful lips speak only words of kindness~

Yes, was just going to post that - they wanted him for the part so badly that they just overlooked the fact that he looked older.
They could've dyed his hair to make it more convincing, though.

I have a feeling the character was suppose to be younger and were going to cast younger but liked Steve Martin for the part. So the line was never changed. That is my guess.

A guy I used to work with went grey when he was six or seven years old, so hair colour doesn't really have much of a bearing on how old you are, as it could start to grey at any time and genetics also play a part in the process.
Furthermore, people could have also LOST their hair by that age, so Steve Martin having a full head of grey/white hair looks pretty damned good.

This message has been deleted.

Steve Martin looked near 50 in this.

Maybe his hair was white thru all that pressure?

I agree with the OP. Based on his looks, they should've made Gil over 40, unless they dyed his hair black (like in Little Shop of Horrors, that made Steve look so much younger).
However, lined up with the kids' ages, it makes sense to have him be 35. Kevin was 8 or 9, and Justin and Taylor like 5-7. Although it would've worked if he were 45 and Karen were younger (she looked a more convincing 35 too), especially since older dads and younger mom's isn't uncommon.
I do agree that lots of 35 year olds tend to look younger these days. But people up to their early 30s have played high school kids in movies for years, so I had a hard time buying Gil as being that young. Although maybe the stress of everything made him turn white early, lol.

Um, no, Steve Martin just went white VERY young. He's had white hair since he was in his 20s.
If anyone boos you off stage, that is simply applause from ghosts.
~Sharon Needles

People aged faster back then, or rather, 30-somethings looked like total adults, not trying to pass as 20 year old college kids

I thought he looked it Or at least what I thought 35 looked liked when I was a kid He really has always had a young looking face with not wrinkles and such He just had white hair, like Anderson Cooper
You people are the disease, but I've got the cure. ~Morgan on "Chuck"

She always looks great.

Mary Steenburgen was only 36 in 1989 though.

Mary Steenburgen didn't look 35, either, and I take it she was supposed to be around that age.
Justice for the 96
-15th April 1989
YOU'LL NEVER WALK ALONE