I agree with the previous post. I didn't start med school until I was 34, and had 14 yrs of enlisted service in the army. I had to fill out an "age waiver" which was basically a one-paragraph letter (USUHS gave me the format even) saying "please waiver me".
The admissions people were very clear in that, while waivers were given out at the drop of a hat, nothing was guarunteed, but there are 3 people in my class who are even older than _I_ am - all with prior service, 2 of them as Os and the other enlisted.
If you're not over 40 don't worry too much about it.