Under section 35-47-2-7(b), it is unlawful for a person to sell, give, or in any manner transfer the ownership or possession of a handgun to another individual who the person has reasonable cause to believe:
Has been convicted of a felony or adjudicated a delinquent child for an act that would be a felony if committed by an adult, if the person seeking to obtain ownership or possession of the handgun is less than 23 years of age;
Looks like it can't be in your name until you buy one at age 21. It would not be legal for you to have someone buy it for you, either (straw purchase).
You CAN carry a weapon that belongs to your brother (or another family member), but can't buy it.
Hope this helps.