If your refund contained certain refundable credits such as the Earned Income Tax Credit, or Additional Child Tax Credit, then the law requires that your refund be held until the middle of February. If your brother's return did not contain these amounts, this could explain why his refund was processed more quickly than yours.
That is one explanation and the most common one this time of year. However, there are a number of factors that affect the processing time of individual returns, and if the above doesn't apply in your case, there isn't any way to know what causes the difference in processing time.