Can a girl be too "loose"?

I seriously doubt that at 25 you have anything to worry about. As I understand it vaginas recover pretty quickly after being stretched even repeatedly for long periods of time. Even after childbirth. I have sex with several women that have had children and none of their pussies have been "too loose."

Being "loose" is something that doesn't happen. The vagina is amazing. You can spit out a 10+lbs baby and still not be loose. It's designed to stretch and tighten. Relax. You aren't loose. It's just something that people say to make us feel self conscious about our vaginas.

The vagina isn't a tube that gets stretched out and stays that way forever. It's muscular and elastic, and generally returns to its shape fairly quickly (activity contingent, of course - childbirth might take a little longer to recover from, or so I've been lead to understand).

If you're truly worried about it, get into kegel exercises. These can be beneficial for any woman, for that matter, so there's nothing to lose by doing them even if you're not concerned.