I'm 47 and recently I laid 52 square meters of ceramic tiles in my house.
Believe me I felt all of my 47 years.

The last time I did anything like that was more than 10 years ago and although hard work it was done without any dramas. This time I really had to push myself to finish.
Yes the years fly by but if you're happy and doing the things you love then that's a great life.
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If you want to find out how "old" you really are try doing something that you did in your youth... Like skate boarding or ice skating.