If he was heading somewhere I'd be alright.. But he shows no signs of doing anything with his life..
Does anyone take interest in his future? Like do you, or Juli, or his father talk to him about stuff? If you let him live in the attic and never engage him, he'll probably just keep on with this stuff.
You don't have to be a parent, just be a big brother. A positive, motivating personality.
Is he good enough to garner BMX sponsorship?