At what age are you considered old?

I heard a remark many years ago that age is a matter of the mind...if you don't mind, it doesn't matter. How true this is. I'm in my mid-fifties. Is that old or not? It depends on your perspective. If you watch a 6 year old prance around, jump and bounce and run. You think how nice it would be to have that kind of energy again. But you watch a kind senior as they struggle to climb the steps or to get in and out of cars and you realize how blessed you are to get around good. So is age all about perception and comparisons? Compared to a 5 year old, 50 is OLD. But sit and visit with someone nearing 90 and you will realize how many good years you have left. So, to me age IS definitely a matter of the mind. So it doesn't matter how old you are, it's what you do with the precious time you are given. Enjoy life to the fullest every moment of everyday. And don't worry about if you are old, just be glad you are alive.