A twink is a young gay guy between the ages of 18 and 21. Some twinks may extend beyond 21 if they look young enough. Twinks are boyish and cute. Twinks usually have little muscle development and I would say no body hair, or at least no chest hair. And I wouldn't say a twink would have facial hair either. The point of being a twink is to look as young as possible.

Check out Boy Alley, it's pretty much got the niche covered:

http://www.boyalley.com/tour1.html

A fat guy in need of a tan would be a Chub or a Bear depending on how fat he is and whether he's got any body hair.

Cheers
dzinerbear