I am 51 and often wish I had stayed in for more than the 8 years I did. I was in the Air Force and when I was in, women couldn't be in combat. I would enlist right now if I could, although, I am a bit of a chicken. I hope I could perform when needed. I think I could.
I've been talking to military people over the past 7 weeks. There are MANY positions that non-physically able people can perform in support -- whether in active or in the rear. It isn't just about sending troops to Iraq or Afghanistan -- the total operation involved IS HUGE. There are support positions which can be ably done by those with the skills thereby freeing "others" who are currently being kept in the rear.
My dad served in WWI, Korea, and was commissioned for Viet Nam. He told my brothers and me what keeps you alive is being "scared". It's when you let your guard down that you don't see or perceive the sniper, mine, or enemy combatant. Ergo, you would perform fine, if called to! :)