The fact that at age 21 you probably don't have as thick a beard as you probably will in 10 years or so shouldn't stop you from at least trying it out. However, as one who made a couple of attempts at early beards and has photos to prove that they looked like shit, don't make the same mistake I did. Do not become attached to every single whisker that grows on your face. Let it grow in untrimmed until it's about 1/2" long and then take a hard look in the mirror. Decide which parts are coming in thick enough to keep and which parts are just going to look scraggly and shave the scraggly crap off. Shave your neck up to near the beginning of your jaw line regardless of how thick it is coming in there. A beard that is mostly neck growth instead of jaw and chin growth will make you look like either Abe Lincoln or an Amishman. If, in the end, you can only grow a pointy little goatee just be happy with it. If it's good enough for the Prince of Darkness it's good enough for you. If you can't even grow a decent goatee, just keep shaving and check back in ten years or so.

Bruce