I'm pretty sure mine started growing around 12-13. Yes, as in 7th grade.
For the past few years I've been keeping it trim and cleaning out below my jaw line and the upper half of my cheeks (so, the beard "flows" into my goatee). After hearing for years from girls that they like "clean shaven," I crack up because I'm usually the only one in the group who has a beard or who can even fucking grow one, and I get more attention for it (at least, I think so). Some guys have patches so, even if it's kept trim, their faces look "dirty" because the hair isn't consistent.
My girl likes it. I don't look good without it.