Just what the heck is there to celebrate about Birthdays

Well, maybe up to 40 for men, I suppose 30 or so for women

After that Birthdays become a day of mourning

Current World average is 67 according to Wikipedia. I think the US is about 77 or so.
To put it into a visual perspective stretch out a tape measure to 77 inches. Put a mark on the tape showing your age and see how many years you might have left.
You Metric people can apply the same principal but do not expect me to understand Metric

In my case my mark will be 63 inches
(much closer to 64 actually). The 14 inches remaining to 77 look rather short compared to what I have already travelled.
Or you can also say after 40 you are on the down side of the roller coaster ride ....... believe me it does go fast.

And have you ever noticed how kids will say "almost XX old", however as you get older bragging about the "almost" factor quickly becomes a thing of the past

In my case I am 63 until I am 64 and not a day before
