I have noticed a "slowing down" in fiberglass (we used at least 6 of the same lamiglas blanks for gills)---it was amazing to wrap a new one up and feel how crisp they were.

The slowing down would take a year or 2 of steady use---I have to believe that graphite slows down also but at a much slower rate.

Im still using the same Fenwick graphite (and boron) spinning rods that are 30 years old after 20 years of tournament fishing and still are among the best i own even after steady throwing up to1-1/4 oz lures.

I cant say that i've ever noticed a slowdown of a graphite flyrod.