"Even with a handful of the Dolphins' youngest players not yet on the field, Reggie Bush couldn't help but notice his rather advanced age Friday.

He's five seasons into what was supposed to be a spectacular career as a running back, and he joins his second team as a bona fide veteran at the age of 26.

"I can't believe it, but I'm kind of one of the older guys," Bush said, rocking Dolphins workout gear, though he can't practice with his new team until Thursday.

When it comes to running backs, a sixth season already can be the beginning of the end. At the very least, it's certainly not the time when you try to redefine yourself. A running back with five years and microfracture knee surgery under his belt isn't supposed to ask for more carries, more collisions, more cuts, more bursts, more offensive responsibilities.

But that's exactly what Bush is doing here. Having spent the majority of his career being thought of as a wrinkle instead of a workhorse, Bush enters his new surroundings hoping to prove he can carry the load.

Five years also is more than enough time for people to formulate opinions about running backs. And the popular idea with Bush is that, no matter how badly he might want to prove to his critics that he can be an every-down, carry-the-load playmaker, it's apparent he's not built for that role.

The numbers will tell you he can't, especially the ones that show his averages drop the more carries he gets."