Yes thats too young, what extra curricular activities has your son been in been involved in during his childhood and teenage years?
What's been his creative club: musical instrument, art?
What's been his social and and skill building club: cubs/scouts, which cadets has he been in since beginning secondary sea, air, army? Has he started work on his Duke of Edinburgh award yet through cadets?
Sport: mountain biking, basketball, football, rookie lifeguard, football, tennis, canoeing, sailing club, athletics - there's lots of sports to try
I take it at 11 your alarm bells rang with sexuality discussions and you cut his Internet time drastically??
Does he have a smartphone with all social media blocked? Do you restrict YouTube, do you have his phone locked with parental controls in the evening so he's had downtime.
If you don't put the brakes on this at 13 years old this is a slippery slope.
He needs a full and interesting life of different in person interaction. I'd be getting him a brick phone for one year and the reassess.
I'd be forcing him to join a creative, social/skill building club and sports club outside of school this week. I'd be forcing him to join school clubs again creative, social and sports. One of each.
I'd make that boy so busy in the real world and so disconnected from online that he'd quickly forget about this.
You're his parent, take charge of this situation before it gets worse. Good luck.