Outdoor Resorts Palm Springs had a 15 year rule but "Pride of ownership condition" overides it. I suspect most use it as an option if a junker shows up. You know, rolling meth lab.
In October we stayed at Shadow Hills in Indio CA across from Sun City. They had the 10 yr rule but never even mentioned it. We were traveling with our 93 Allegro Bay unit.
Super nice campground staffed by great workcampers who were very nice and personable. Good Sam discounts but prices were on par with most upper tier CGs in California.
I could be wrong. But it seems to me, that if Hic John Doe pulled up in a 12 year old rig that was on it's last legs 10 years ago, and was refused entry. Then he could point to a rig that was just as old and holler discrimination and win, if that park had some in it that were that old.
It also seems to me that most RV manufacture's, design their rigs to self destruct in less than 20 years IMHO.