@ Chris & George - Not being a musician, I don't have unknown 14-yos contacting me on FB (and I don't go round contacting them myself). But I do have youngster "friends" on FB, in all cases children of real-world friends, but they all had to ask me (prompted, presumably, by seeing me on their parents' own friends lists); and though I accept them if they ask, I never approach them. (They're all, as it happens, kids of people I know from living in France, where the social life is more outdoors and multi-generationally inclusive than in the UK.)
This rule of mine also applies to people who are now adults (including my niece) but who first met me in real life as kids dragged along by their parents. If I first happened to meet someone as a 9-yo kid or, in the case of my niece, a baby, even if they are now in their 20s that early contact was not their choice or idea, and so I just leave it to them to friend me if they want to.
There are occasions when FB suggests I friend someone who has 14 friends in common; if I only vaguely recognise the name I don't bother, but I can see how one could be absent-mindedly prompted to make a friend request to someone you actually don't know.
I also generally don't accept even direct friend requests from people I know who haven't posted a picture, though I do if the picture is of a hat or their dog or something. I'm not sure why I make the distinction... maybe I think blank, default silhouetted head requests are by some bot or chancer?
If I do send a friend request I always include a personal message.