Did he turn 19 on March 18 in 2022 or 2021?
If he was still 18 on December 31, 2021 you can claim him on your 2021 return.
If he was 19-23 you can claim him if he was a full time student.
If he made less than 4,300you can claim him no matter how old he is.
If you can claim him he has to check the box on his return that he can be claimed on someone else's return. If he didn't then he will have to amend his return and you will have to mail your return this year.
Who can I claim as a dependent?
https://ttlc.intuit.com/community/credits-and-deductions/help/who-can-i-claim-as-my-dependent/00/267...
Who you can claim article
https://turbotax.intuit.com/tax-tips/family/rules-for-claiming-a-dependent-on-your-tax-return/L8LODb...
