Bump as many topics as you want, don't mind the post date. One condition:

Make sure you say something that contributes to the forum!
Give useful feedback, ask intelligent questions, and use proper grammar!

Bad bump examples:
cool.
these are OK
This sucks you guys are noob!!!11
Whaen is this mod goin 2 B released!1

Another thing, if you're not staff, don't scold bumpers.
Often times, it's the one who bumped the topic that made a more useful post than the one scolding the guy who did the bumping in the first place.