Re DRB checks - both of my older children started doing voluntary work at 14. No check was needed before 18, so my younger volunteer still hasn't had one. He helps with Beavers, as someone else suggested, but here you have to be 14 to do that. He also has a paid job coming into contact with children but no check needed for that either - probably because he is never alone with the children. So I don't think you would have to worry about that. In fact I just checked and the minimum age you can be asked to have one is 16, so that isn't a concern.
Animal charities wouldn't need one either (though if quasimodo's thread on animal rights takes off, maybe that is coming next!). So maybe an animal shelter or somewhere if he is interested in that? And I bet if you could find a home for the elderly they would really love to have a young person in to chat to - chronic loneliness in the elderly is a real indictment of our modern society I think.