In reply to Removed User: I agree, apart from obvious damage, I think you know in your heart when it's had enough.
I retired mine last week, was damaged so I cut it short, but the rest of the rope seemed to be really soft, folded too easily, knots became a nightmare to undo, it lost it's dry treatment, and at 5 and a bit years old I decided I wasn't going to lead on it anymore.
Still be happy to top rope with it for a bit longer I guess.