* Relationship Test: This is met as he's your brother.
* Residency Test: This is met if he lives with you for the entire year.
* Support Test: You must provide more than half of his financial support. This includes tuition, food, housing, clothing, etc. Just providing housing isn't enough if he has other significant sources of income or support.
* Gross Income Test: His gross income for the year must be less than $4,700 (for 2023). This is a crucial point. If he has a part-time job and earns over this amount, he likely won't qualify as a dependent, regardless of other factors.
In short: While being a full-time student *helps* because it lowers his likely income, it's not enough on its own. You must provide more than half of his financial support, and his income must be below the threshold. If he has significant scholarship money or other financial aid, that also impacts whether you provide more than half his support.
You should consult the IRS's official publications or a tax professional to determine if you can claim your brother as a dependent. The rules are complex and fact-specific.