Not sure. I know you have to be 16 years of age and older to drink beer and wine and 18 for hard liquor. I imagined it would depend upon the club, but my guess would 16 or 17 years of age and older.
It really differs. At most 'hip' club places they'll require you to be 18 or 21 - or even above. You can get into bars and some smaller, less popular and probably tourist-ridden clubs at 16, but don't expect much. When you're there, be sure to check out Jimmy Woo (18-21 policy, very popular and 'hip&trendy' if you will). You also have Cineac, which even enforces a 25+ policy. Less trendy but equally fun are the places which have more students. Dansen bij Jansen, Panama. Another really good place to check out is Bitterzoet, especially if you're into jazzy music, you should never miss thursday nights there. Indeed - 16 to drink beer, 18 for hard liquor. Take your ID with you when you go out, people may ask to see it. Any other questions, just ask
Be sure to take it with you. Bouncers have a habit of being selective to whom they ask to ID themselves, but it might just be you.