My ds12 is lovely and has lots of friends at school but I wouldn't call him sociable as such. He hasn't bothered contacting any of his friends to hang out over the holidays despite us offering lifts, saying he can have friends over etc.
I see kids he knows out in the area but he isn't interested in joining in. He tends to hold a bit of a grudge as in if he's ever had a falling out with a kid he simply won't entertain them again which is fine I guess, he has boundaries but I just think he's a bit young for grudges!!!
We went on holiday recently and I kept encouraging him to try and make friends with other kids in the pool but he's just not like that. Shy perhaps, or just not interested.
At home he's quite happy in his own company playing games, reading and watching films with dh and I but I do worry a bit. He messages friends from school (sadly his school friends aren't local to us but as I said the offer to facilitate seeing them is there) but doesn't see them other than at school.
He plays in a football team so it's not like he's never around kids his own age I just feel a bit sad he's spent most of his summer alone.