Both my sons have autism.
My eldest son was in nappies until he was 6.
He was very aggressive. He would throw himself around, hit, bite, kick. He broke my nose. He wouldn't allow you to cuddle him. He'd go rigid. If you went a different way to the shop he would completely melt down.
We were told that he would never learn to talk. That we should teach him makaton. That we should put him in a special school. We were accused of being in denial when we said no to that.
When he was 7 he started to talk - at that point he sounded like a toddler. He continued to have soiling accidents until he was 10. We were told the best we could expect would be he would be able to live in a flat with support as an adult.
I remember posting on here from when he was a toddler and we were going through all that.
He didn't have any friends. When he was little the NT kids were 'kind' to him primarily for the praise it got them from teachers.
Then he got to secondary school and all pretence stopped and he just got bullied.
We did all sorts. Involved him in clubs for kids with autism, that sort of thing. He made a friend and that was wonderful while it lasted but the friend grew up and no longer wanted to be friends because my son still liked to be 'silly'.
He is now 23. He has his driving licence and a car. He is about to finish his degree. He is in the process of buying an investment property overseas.
He attends a social group for autistic uni students, they get together for a range of activities.
Socialising is still hard for him but he is putting himself out there. He is emotionally immature for his age and has stims and obsessions. He is and will always be autistic. This is who he is. He would make anyone a wonderful friend if they would just give him a chance and accept his autism as part of him.
So massive achievements for him in many ways but other people's prejudice a barrier in others.
My advice is look for social clubs and groups for autistic teens. Help him build friendships there. It's a waste of time and effort hoping for friendship from NT kids. (This is simply my experience.)
My younger son is 22 and going through significant challenges but we are confident we can continue to support him through them.