Too much water can kill you , despite body being made up largely of it. Too many egg's can be bad, but in general if you're eating them as PART of a HEALTHY diet its not bad. I wouldn't recommend 6 egg's a day to go with a load og greasy bacon, heavily buttered bread and whatever else. They "could" cause high cholesterol if you had a lot of cholesterol already or intact a lot in the rest of the food you eat. But not all cholesterol is bad for you, and you probably have an inavoidable and maybe needed level of the "bad" stuff aswell.
AS for not eating as many after you hit 30? not read that before, but theres probably a study out their linking egg eating to everything from being run over to peadophilia. Theres a study for anything and as long as there is a study, proven or not, reliable or not, someone will run around screaming its true. You won't live forever anyway, all this, thats bad, thats good, thats bad crap that changes weekly, at the end of the day its too late, you've already eaten some of everything that might kill you at some stage, so what, so has every other human being who ever lived(and ever will).