If you were not a full time student, they cannot claim you because you had too much income. The income limit for a 21 year old who is not a full time student to be claimed by a parent is $4200.
Here are the requirements:
1. The person cannot be your qualifying child or the qualifying child of any other taxpayer. A child is not the qualifying child of any other taxpayer if the child's parent (or any other person for whom the child is defined as a qualifying child) is not required to file an income tax return or files an income tax return only to get a refund on income tax withheld.
2. The person either (a) must be related to you or (b) must live with you all year as a member of your household.
3. The person's gross taxable income for the year must be less than $4,200 in 2019.
4. You must provide more than half of the person's total support for the year.
5. The person must be a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico.
