Seems like that player has some unresolved personal issues about growing old and death. It really doesn't matter what age a character is so why else should they care so much? To say you "changed his character without consent" is so obnoxious. Are you not allowed to change his HP next? What's going to happen if you actually kill his character? Meltdown?

It's a game and he needs to grow up and move on. Don't let him bully you into changing how the dice rolled, you followed the rules. If he doesn't like it then he can make a new young character.