Ok so as the parent of an AudADHD child (albeit different issues) - these are my thoughts.
consider meds but they can cause more problems for kids who have autism too. But seek a referral to CAMHS/ ND team. Or look at private intervention- if you were considering private schooling, this could be an option.
ND children are emotionally younger than their chronological age, but can conceal this because cognitively they appear their age , if that makes sense. But I think you need to respond in some ways as if he were younger - certainly in terms of boundaries and freedom.
Decent quality food and exercise can make a huge difference. If he is living on crap, as many teenagers are, you need to address it and ensure he has a balanced diet, lots of protein, minimal UPF etc.
What is his sleep routine like? We used melatonin for a while - initially prescribed privately and now we buy it but she only uses it as and when. She likes a bit of nurturing in the evenings - if she is still wound up, I may run her a bath with nice oil/ magnesium salt / candles/ talking book. Or bring her toast / hot chocolate in bed without asking. She still likes it when I read to her (she is 14 and more than capable of reading ).
I would be sitting him down and talking to him. Tell him you love him and you are not prepared to see him on the road he is on which will lead to prison or whatever - be totally upfront about the risks. And that consequently, things will be different. You are going to agree a new routine as a family that he contributes to and that does not involve him hanging around the streets.
He can either choose some things he wants to do or you can choose! I would be looking at:
Martial art - maybe Muay Thai or something like that. Not boxing - it’s aggressive. But kick boxing or cross fit is ok. Chat to some local instructors- you are looking for a bloke who can talk to boys on their level but also be strict etc. I would look for a very small group, or 1:1 - even PT.
IME, team sports for ND kids is a no go! My daughter boulders - but I go with her - that’s really important. Great for strength etc. If you live somewhere with choice , go for a smaller one, or a more serious one. In our area, were have a large noisy one that’s full for kids, and one that is generally full of young, earnest adults who really encourage her. It attracts a nice crowd.
i don’t know much about cadets , but my nephew, also with ADHD and autism, loves it.
i also go hiking with my daughter and wild swimming. Somewhere interesting with caves etc. Or we explore abandoned areas. She will often choose or plan routes. Depends what is accessible to you though. Ooh and nighttime walks to look for foxes or scare ourselves silly!
Board game cafes as a family? Or if he has any nicer friends? The ones here do decent pizzas and are open in the evenings and can be a lot of fun.
We meet as a family every Sunday evening and plan the week. Including the menu, activities, family film nights etc, who has what on etc. All written up. Pictorial routine can be really helpful! We had one until she was 12 or so - a step by step routine and weekly plan.
Lots of time with both of you.
Try and explore what he likes and what underpins what he doesn’t like - eg, anxiety, noise/ light / crowd sensitivity- I wondered this as he is roaming the streets. Eg , my daughter doesn’t like group / team activities or too much noise or crowds.
what does he use his phone for? Is it closely monitored - it needs to be. No tech in his room.
education - what is he studying? What does he enjoy? Do you know what his curriculum contains for next year? Engage with him about it. Read the poetry and English texts too. See theatre and film adaptations and swap views on it. Same with the other subjects .
Look, I know you can’t drag him to things or lock doors. You have to try to engage him - show him documentaries or films that depict the risks of the road he is on. Hang out with him for a bit first. Muck about! Play! Be curious about him - why does he like them , what does he like about what they do? How can that be replicated more safely.
Community involvement and responsibility. Does he see you and his dad get involved with this? Taking a bag with you to collect rubbish? Shopping for a neighbour?
I would be clear that it is non negotiable and that any money, monitored screen time etc is to be earnt. He should be doing jobs, but should be able to contribute to what he wants to do. So my daughter hates smells so no bins or litter trays but she is good at cooking and dusting. But I wouldn’t cancel planned activities- even things like cinema trips. He needs to see alternative ways to spend his time.
Lots of praise when earned.
If he doesn’t comply, I think I’d take him out of school for a month, go off sick, and book a remote cottage somewhere very rural with hiking, books,
games , no WiFi etc. I know it sounds mad but it seems to me to be a combination of getting to know one another and keeping him safe/ breaking a cycle.
I have waffled on and on - but I hope some of it is helpful. It is still a challenge for us as a family but we are learning. Communication is key!