Looking for advice: how to help 19 year old socialise with new people (uk)

My child attended a specialist school for autistic kids from age 11 to 16 and the school has a section of the local college too for students to do their A Levels and vocational courses too. It's years 12 13 and 14, so 16 to 20ish year olds.

My child is in year 13, he's got equivalent to a levels in qualifications and he's for sure out grown that environment when it comes to his improvements in harnessing his intelligence and gaining new abilities. He's also clearly outgrown his peers there.

He's able to go out into the city at weekends and stuff and his peers (that have been his friends since 6years of age) are not able or allowed.

I have stated that he'd only need to stay on for their year 14 due to social reasons. The teachers agree.

He could move on to the mainstream courses at that college which would cater to his interests more and put him in a room of kids his age with similar interests. I am really wanting this to happen but he'd need to be accepted and he'd need to accept it himself. That is the easiest and most likely way I see the issue being resolved.

But if he needs to do year 14 at the same unit I'm struggling for other options to get him around his peers in a way that would be conducive to building friendships.

There's not one youth club, he refuses sports vehemently and there's no other activities available where kids his age regularly meet. Unless he joins a gang.

I know this may be as simple as "He's ready for mainstream education so make it happen." And honestly this is my game plan.

Im just wondering if anyone has guidance and advice if it doesn't go so smoothly.

I don't like stating this but it's relevant to the issue: his autism is not at all obvious to anyone but himself and those that know him. He was non verbal til 5 but has just flourished ever since. Especially during puberty.

However he is terrified of job interviews and he's not ready for that yet at all. So a part time job isn't viable.

Any help at all or reassurance with the mainstream class route would be greatly appreciated