Callistemon, I know where you are coming from, but this puzzle has only 4 lines.
If it was to be a sequence, that would absolutely be correct and would have said so.
I too overthink and tend to look for more than is asked. 
However, I never said it was a sequence. 
What did you you think you would have by your current age that you don't?
Only 50% of middle age adult manage more than 1 brisk 10 min walk a month.


then?

calm down dear, it's only an advert for the algebra which is yet to come.