What is the latest breakout career that we can think of?

[tryfuhl]

I'm talking about a player who has the longest experience, resides in mediocrity or less, and then all of a sudden breaks out for the rest of his career? This should be largely independent of outside factors.

I have no doubt that players can be listed, maybe Kurt Warner, though he certainly had a break in his productivity, but an example as such opens us up to the possibility that teams can do players injustice.

Unfortunately, this ties greatly into the QB debate. There are QBs who arguably could've done much better without given situations hampering them, but what players rebounded from this?