amir_st0ne saidhow old must one be to fully grow a beard?
Another thing to think about is what style of beard; it doesn't have to be a full beard. When I was young mine was spotty/sparse below the cheeks.
A beard style that I love, and which fortunately is no longer all the rage (so you won't look like a clone if you wear one), is the van Dyke, which is also commonly called a goatee. That accommodates/compensates for the lack of fullness on the cheeks. To me, a goatee is just on the chin, and when you have a moustache with it then it's a van Dyke. The moustache and goatee must be connected. Purists would probably call the style where the moustache flares out on the sides a van Dyke; i.e., the 3 musketeers style. The downside to the van Dyke is that it gives you sort of a devilish look, which I think is part of its allure.