I've got mine down to 20 now (although I haven't played it in a while! After I got 20 and put the rest of the family to shame, I got a bit bored of it
)--the first time I played it though, I was apparently as fit as a 52 year old (by the games standards, at least). Just worked my way down to 20 after I got used to it.
Guess it wasn't as bad as my 11 year-old cousin... he got told he's as fit as a 76 year old.