Yep. The answers have been given. Nothing more needs to be said, really.
But here is how I would explain it:
The blade, as long as you do not break the blade, it will last forever. I have a few blades from 1991. They are still awesome. I don't use them because, well, I want to keep them how they are.
The rubbers, there have been a bunch of good ways presented for when to change rubbers. I would explain it this way: when the rubber stops grabbing the ball, then you might want to think of changing it, unless you were using an antispin type rubber. With antispin less grip is what gives it the properties it posses.
And the issue about grip of rubber as the measure for when to change it, that only is valid if you know how to spin the ball properly. So, someone more on the beginner side can use a rubber for longer without realizing that the rubber does not grip the ball since, usually, lower level players make more direct contact and do not generate anywhere near the amount of spin that someone who has higher level technique would.
If you feel the rubber is not grabbing the ball and spinning it, then it is time to change the rubbers. When that is the case, usually, you will see wear in the topsheet that exposes the pimples as Yogi said. If, after 7 years, the rubber still grips, no need to change.