I just had to reply to this one (and registered at last to do so). I am 38, and have been playing sice Civ I, probably 10 years now?
The fun part is my 8 year old son is getting into it now in a BIG way! You are never too young, or too old. A long attention span is rare for one so young, but then again he likes Quake too.
My wife used to complain a bit about the amount of time I spent on my computer. Now I use my computer to make plenty of money to pay for the house, pool, school fees, etc, so no complaints any more!
Cheers