One of the Bible's greatest truths is that God never gives up loving us, and He always stands ready to forgive us—even at the last moments of life. The Bible says, "He is patient with you, not wanting anyone to perish, but everyone to come to repentance" (2 Peter 3:9).
I hope you will rejoice, therefore, that your brother is apparently facing his need of God—even at this late date. Yes, it is sad that he has spent his life away from God; his life would have been much, much fuller if he had given his life to Christ when you did. But soon he will die, and it would be tragic for him to go into eternity without Christ. God is able to do what we cannot do, and He is able to change his heart and cause him to turn to Christ.
Pray for your brother, and ask God to help you point him to Jesus. Don't let the past get in the way; don't approach him with an attitude that says, "I was right, and you were wrong." That would only create a barrier, and that's the last thing you want.
Instead, assure him that you love him and that God loves him also. Then encourage him to open his heart to Christ. The Bible's promise is true: "Believe in the Lord Jesus, and you will be saved" (Acts 16:31). It was true for you over 70 years ago, and it is true for your brother today.