I don't see why you should be worried. If they decide to spend that much time on the game then I'ts their business. Who are we to say "No, stop leveling. For god's sake don't get 99."
Look, Jagex put food in the game for one obvious reason, to keep us alive. I don't know about you, but if I have the resources to keep myself alive, I'm gonna use them. If that makes me a noob, so be it.