He must file his own tax return if his earned income was over $6300, or if he had net earnings from self-employment of at least $400.
Even if his income fell below these thresholds, although not required he'd have to file a return if he wanted a refund of any withheld taxes (as explained above by xmasbaby0).
If he does file his own return, that does not preclude you from claiming him as a dependent if he meets the IRS criteria.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
