Hi Gwen,
My job is helping people with Disabilities and health problems find and sustain employment. As Moonmaiden says, the first thing he should do is sort out his benefits situation to make sure he is getting all he is entitled to. Since the Disability Discrimination Act there is no longer a registration of people with disabilities, rather a person is considered disabled according to the law if they meet the criteria laid down in the act. Have a look
Here and you will be able to see a breakdown of the definition of disability.
The Unit that I work for takes referrals from the Jobcentre, health professionals etc, but we also take self referrals. It may be that there is something similar in the area your nephew lives in. The Association of Supported Employment website, which can be seen
Here , has a member locator. You could see if there is a member organisation in his area and give them a ring to find out if they take self referrals. If they don't, ask them from whom they do take referrals; it may be a GP can refer him, or similar.
Also, although the Jobcentre Plus say they can't help him because he is not 18, the Disability Employment Advisor in his local Jobcentre should still be able to see him and offer assistance. To make contact with the DEA, phone the Joobcentre, ask to speak to them and make an appointment for him to see him/her.
I hope this helps, but if there is anything more you would like to know, please feel free to PM me :)
Lesley