to be a dependent he doesn't have to be a student if he was under 19 on 12/31 or if he was 19 or over on 12/31 he could still be your dependent if 1(his gross income was less than $4,700 and 2) and you provided over 50% of his support
you can use this iRS webpage to check
https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent
