Granted we never played Epic levels until that last long campaign, but I've never stopped a PC until at least 18th level in 30 years of gaming and at no time was there a need to rewrite rules, the rules are there in the books, no rewriting necessary, and that's with 1e, AD&D, AD&D 2e, 3e, 3.5 and now Pathfinder RPG. Where are these rules that need rewritten?
No conscious designer, said, "hey, you're doing it wrong, you're supposed to stop at 13th" - that's not written anywhere in the books, I've never got a notification from the publisher to imply such a thing. I know on lots of forums this kind of thinking is believed by lots of people - but I've never had such a belief or felt that the games were so broken as to not be able to handle that.
Every edition has PC generation tables going to 20th level, is that a mistake, should they have only gotten to 13th and stopped?
You play what you think is normal and leave us guys who actually go by the book (and not rewriting the book) to play whatever the game allows. It allows at least 20th level, and though only available in the 3.0 version, there is an Epic Handbook - no matter how broken you think it is.
Personally once my character is at 20th, I don't really want to keep going, but I am one in a party of six players, so if they want to keep going, I keep going. One of our players is a Psionicist/Monk 43rd/42nd (that's 85 levels) though not my preference, it is for our group.
I'm glad you have an inside on what the designer's really intended, because I've never seen such nonsense in any of the books, nor heard a designer make this official claim on any forum/website. I think someone has been telling you "stories."
GP
PS: except for the fact that we use D20's for initiative, we don't even have "house rules", we go by the book on everything.
PPS: how age affects all these high levels, you ask. All these levels take time to acquire, and if you're nolonger taking age effects, especially for martial classes you are breaking the game. Age effects come into play in our high level game - how would it not?