You can continue to claim him as long as he is a full time student under age 24 and he doesn’t provide more than half of his support. He must file his own return to get back any tax withheld or if he has a filing requirement. He can only contribute to his IRA up to but not more than his earned income.
This is guidance for a dependent’s filing requirement.
https://www.irs.gov/publications/p929#en_US_2020_publink100066042
