Possibly, your brother meets the age test of being under 19 at the end of the year, not sure about the support.
You can claim a dependent on your 2017 taxes as long the following requirements are met:
- You cannot claim a dependent if you, or your spouse if filing jointly, can be claimed as a dependent by another taxpayer.
- You can't claim a married person who files a joint return as a dependent unless the joint return is filed only to claim a refund of withheld income tax or estimated tax paid.
- You cannot claim a person as a dependent unless that person is a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico.
- You cannot claim a person as a dependent unless that person is your qualifying child or qualifying relative.
Qualifying child tests
- The child is related to you as - son, daughter, stepchild, foster child, brother, sister, half-brother, half-sister, stepbrother, stepsister, or a descendant of any of them.
- The child is under the age of 19 at the end of the year (under age 24 if a student), and younger than you (or your spouse if filing jointly).
- No age limit for permanently and totally disabled children.
- The child lived with you for more than half the year (exceptions apply).
- The child provided less than half of his or her own support for the year.
- The child must not be filing a joint return for the year (unless that joint return is filed only to claim a refund of withheld income tax or estimated tax paid).
