You have the right to recover the money from your younger brother if you have given him for a lawful purpose. However, it was not a contract under which money was given. But you have a right to recover the money with interest or without interest.
You should file a civil suit (money suit) for the recovery of money from your younger brother. In this situation you should send a legal notice to him and give him a chance to settle the matter out of the court. Thereafter, you can get back your money from your younger brother.