Social Security benefits are based on the number of years you have worked and the amount of money you have earned. It is not based on whether or not someone is a dependent.
If social security is his only income, then he has passed the income test. However, he still has to pass the support test. You would have to provide more than half his total support. That means if his benefit is worth $15,000 per year, you have to provide $15,001 exclusively to his support.
