I mostly like Mr Shugarts advice but I would refine it a bit in saying that there is no reason you can't be a little selective and just enjoy the better stuff.

FWIW I can definitely say that I've had FAR better sex AFTER the age of 50 than I had before. Yes OK there was a divorce involved etc. but the point is that age doesn't mean life can't be even better AFTER the age of 50 than before. Even if you are still married to the same woman the right attitude and commitment can absolutely lead to the best of everything in your life not just sex.

The best thing about being older is that you hopefully are mature enough to really appreciate all the best things. ;-)

Mark Twain said what I was trying to get at a bit more eloquently:

"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." Link

As others have said, health, family, friends, doing things you enjoy and make you fulfilled. Yesterday is the past, tomorrow is the future. Today is the present, treat it like the gift it is.

And to all you old guys with young'ins... welcome to the club! I'm 56 with a 7 month old son. My friends tell me it's the price I pay for getting remarried to a young hottie. I'm not complaining :-)