Was he a full time student? If he is under 24 and a full time student you can still claim him no matter how much he makes. If he is over 18 and not a full time student you can only claim him if he made less than 4,300 total for the year. You can only get the first 2 stimulus payments for dependents under 17. No age limit on the 3rd one.
Who can you claim
https://ttlc.intuit.com/community/credits-and-deductions/help/who-can-i-claim-as-my-dependent/01/267...
If you can not claim him then he can file independent and get his own stimulus. He can amend his return.
