You could be the oldest twenty years old, or the youngest seventy years old. It's up to you. Live your life and take care of yourself regardless of what age you are: it's just a number. You are same person in your twenties, it is still you in your thirties, then in your forties, you are right there. How about in your fifties? Are you still the person in that body? Of course you are! And you would remain that person in your sixties and seventies and eighties and nineties and beyond.