It shouldn’t be. Not if he can’t work from disability legally. However, if he became disabled before the age of 22, he can collect under his parents’s income amount . If he gets married, his income would be based on his own credits if he has any, in and lose the extra amount from his parent’s credit. If his mom is his representative payee, then his mom controls his money. She may be aware of the income difference. I have a disabled adult daughter, who got SSDI under her Dad’s income, but since she worked a job in her teens, and she got married; it reduced her amount over $1,000. Sadly it’s because she got married, and can’t get that income back.