The mind growing old

I wondered whether one's own mind, like one's body, ages inexorably.

I don't think it's unstoppable, after all I'm still a mental adolescent at my age (young adult to adult).

On the other hand, I also know many who have become quite bitter with age and who can no longer take a joke.

What do you think? Is it normal for the own mind to grow inevitably old with the passing years?