gk404 - I am a 28-year-old full time worker, and there are at least 2 others in my platoon (all infantry folks) who are older than me, currently on my basic course. The other platoon, which is all armour/eng/arty people, has at least a handful of older lads.
So far, no one is finding it too much of a problem, except, of course, for the PT. It‘s not that the PT is necessarily that hard, but at least one of th eolder guys in my platoon has stated aloud he knows he needs to work out more on his own time to meet the standard.
Me, I am just happy if I can keep up on a run, and I usually can.. My weakness is pushups, and so I try to do those on my own time when possible.
Again, the average age is 17-19, with a few early 20s mixed in, but not many.
What is MOST gratifying is to see people much younger than yourself falling by the way side, holding their sides and wheezing, after only a minimal warm up run.
Older guys usually know the "lessons of life" such as: Don‘t try and impress everyone by running fastest/hardest early on -- take your time and pace yourself.