Yes, you are right, and I sincerely hope your nephew will stop and think again about the path he's taking. The Bible warns, "There is a way that appears to be right, but in the end it leads to death" (Proverbs 16:25).
Does this mean God won't forgive us if we've lived a life of sin, but then sincerely repent and turn to Christ just before we die? No, of course not. As Jesus was dying on the cross, one of the two criminals who was being executed with Him asked Jesus to save him, and Jesus forgave him and promised him eternal life (see Luke 23:39-43).
But how do we know we'll even have an opportunity to repent? Our life may be taken in an instant, and then it will be too late. In addition, the longer we live a life of sin, the more calloused and insensitive our hearts become and the harder it can be for us to admit we need God. Yes, one of the criminals dying with Jesus repented, but the other one never did.
Pray for your nephew that God will give him a desire to resist the crowd and put his life instead into Christ's hands. Pray, too, that God will make you an example to him of Christ's love and joy, and also give you opportunities to share your concern with him. Jesus warned, "Wide is the gate and broad is the road that leads to destruction, and many enter through it" (Matthew 7:13).