I think it will pass. I actually finally succumbed to getting a facebook account because my nieces convinced me, so my first three "friends" were 13, 16, and 18 year olds.
It's been ages since I've had a 15 year-old girl suggested as a friend. I think the algorithm looks at your web of connections and it tends to suggest people that you have a couple of different connections to and, as it turns out, not many of my other friends are friends with my nieces's friends, and those that are are almost all blood relatives, so I can't duck 'em anyway.