At 16 they are treated as an adult's application for DLA. Under 16 you have to prove that a child needs more help than another child of the same age who does not have your child's disabilities (there is a proper definition but that's the gist).
Over 16 you have to prove that they need 'attention' and / or 'help in geeting around' as Aspergers applications are judged under the mental health criteria for DLA.
I've been claiming for son since he was 16 - we are now on his 2nd renewal.
The best way of doing it is to write down absolutely everything on the application using extra sheets of paper instead of trying to squeeze a complex set of problems into the 2 square cms provided on the form. My best effort submitted 72 pages - Honest!
I also enclose all the medical reports etc we have and pick out bits in them to elaborate on by describing his specific difficulties. presumable yours has not seen any 'professionals' so you would have to rely on someone endorsing the application. The DWP may contact your GP for further info. If you're turned down you can always appeal.
You live in my area and I use WECIL at Fishponds - west of England Centre for Independant Living - google them for contact details. They will sit down with you and help you fill it in if you want. Much better than the CAB around here who are hopeless and insist you attend an appointment with CAB advisor who iknows nothing about DLA just so they can decide you need another appointment with a Welfare specialise CAB . Grrrrr!
I'd say go for it. If he's not in full-time eductaion try incapacity benefit inyouth / income support (although you'd lose your family allowance if he claimed it himself / JSA too.
DLA is a 'gateway' benefit from which much of the assistance he will probbaly require in later life depends. ie. DLA qualifies him for an assessment for Diasbaled Students Allowance in Higher Education and for Housing Benefit (LHA) if he attends a Uni away from home etc etc etc.
My sister is an adult with AS and gets DLA, but that's because she has lots of mental health problems e.g. depression along with it and can't really live independently.
It's like the child forms: you get it if your needs are over and above someone without that disability. Given that your sons sound very independent, I'm not sure he'd qualify, which just shows how much he's moved on.
A friends son gets it at 17, but they losta fight to get it on his behalf and it goes to him- bear in mind that he has the same anger issues as ds1 but s a grown person. So he gets it, goes out and gets hammered then turns up aggressive .
They've temporarily ahd it halted whilst they apepal theat decision but its not looking good.
Mention on the form that he's scared of visitors, its still worth a go- unlikely they will visit adn if they decided to you could state that as a reason to witdraw claim then, at least you'll have tried.