Most 40 year olds will be laughing inside when screamed at. A smart DI will find other ways to rip him down.
e2,
My guess would be to use the older recruits as examples for the younger ones.
Drill sergeants are alot of things, but dumb ain't one of them. They will recognize the best way to both teach the older recruit what he needs to know, as well as utilize the same recruit's knowledge to best effect.
BTW, does anyone else still get a little nervous at the sight of a "brown round" coming your way?