for enlisted guys...in some cases, i think, yes.
go NS, boy -> more boy.
if people treat you like a child, sooner or later you act like a
child. if you act like a child, sooner or later you will become a
child!
it's true that in the army you learn a lot of useful things: firing
a rifle, digging holes in the ground and then filling them in,
physical and mental endurance, using make-up (camo), and so
on.
But I think it tends to teach some bad habits as well:
1) "just do what you're told" mentaility
2) evading personal responsiblity
3) doing the minimum - no more, no less
4) acting skills, e.g. "pretending to be busy"
5) swearing
6) and more...
obviously, not the typical description of a "mature adult".
For those in leadership positions, or in positions where you have
to activiely think or use creativity, it's not too bad, but for the
rest of us, well... 
disclaimer: this is based on observations in the korean and us
army. (i'm from korea; used to live in singapore before). but i
don't suspect it's any different in the singapore army.
