Age: I'm fifty-four years old I'll have you know! Its too late for me to be embarking on a brand new way of life.
Youth: Perhaps you are right. There's no denying you have become set in your ways. But it's not too late to consider your "future lives". So, you may have made the mistake of ceasing to grow, but you can still use the time you have left to tell others of your mistake, and help prevent them from making the same blunder.
When does old begin?
We are truly old only when death is near - and at whatever age this may be. The idea that it is possible to die young is ludicrous. We die at the end of our lifespan and not before. Life always runs its full term: how can it be otherwise?