For most people, the real physical deterioration doesn't have to kick in until age 65 or so (plus or minus). But you do have to show up every day and hit it hard. In the last triathlon I raced there were men in that age group still finishing with fast times. And they're not genetic freaks either, just consistent.

I don't know, I think if you are a body builder or elite athlete there is plenty of difference even at 45.