It's what I did...actually just before I turned 18.
Granted, the world was a little different in the 90s. My youngest brother is considering enlisting, and while I'd be proud as punch if he did, I'd also worry about him. A lot.
I was 17yrs-10mos, give a take an hour or so.
My brother was in the Air Force for 22 years, and my husband for 10, and that's just in my generation. (I was only a civil servant :-).
If Anoreth thinks the military is the right choice for her, we'll support it 110% (in public) and worry ourselves half to death (in private)!