No, his parents have not been claiming him. The parents have two children - a daughter with spina bifida, and the son. The daughter, interestingly, works part time at a local library, so she files her own return. The son has never found a place in the world, so to speak. 

I agree about testing later in life, but the family is very old school, and they just think he marches to the beat of his own drummer. Which he does. 

I've long worried about both adult children when they face a future at some point without their parents.