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.
At present you want to get back the money from your younger brother hence, it proves that it was either an unsecured loan or not a gratuitous act.
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.