Shows your age in the global mode line as a reminder to squander less
of your brief time on this earth.

Your age is shown with two decimal places so you can witness it
increasing every 3-4 days.  People commonly regard themselves as N
years old until the day they turn N+1 years old.  The decimals remind
you that this is a false comfort: many N-year-olds are already closer
to being N+1 years old.