Aspergers often goes hand in hand with delayed sleep onset. It is not like classic insomnia, even if worry can happen because you are scared for the next day on that little sleep. My own issues started at puberty. I never got my hours in because I could never fall asleep on time. At the end I could fall asleep not way way too late but that was just because of chronic sleep deprivation.

If using melatonin, take breaks on weekends, that stuff might stop working otherwise. Also don't give too much to a kid.

Also know that Aspergers also goes hand in hand with autoimmunity and melatonin can trigger or worsen it. So it is not totally without risks. But IMHO sleeping on time is more important.

Routine actually does not fix delayed sleep onset, it just creates chronic insomnia and might superficially look like a fix.