Hmmm don't know how you can avoid that. When you get to be about a little older than I am there is not much else left for you! But when I was young I remember thinking that to be 45 would be positively ancient and I couldn't even get my mind around the idea. Now I am almost 61 and life goes on and I am still living and still enjoying many things I expected I would have been all done with by now. You adjust.
Usually due to the pain and loss of maneuverability that go along with it.
We all know that we can't help but to grow old (unless you've discovered a way to stop time). What these people mean is to enjoy your "youthfulness" while you can, because it won't last as long as you think it will.