I have driven my 14 year old Tiffin Allegro Bus from Orlando Florida to Deadhorse Alaska with over 2 cumulative nights on the road. I have seen these rules in many camp grounds over the past 3 years but I have never been challenged due to the age of my coach. I keep my coach in excellent condition and we are generally only two older travelers so that may also factor into the process. I have seen one family of 4 in a good looking older coach being refused a spot, but I was only vaguely aware of the happenings and do not know the other circumstances.
It is my personal opinion that if I am ever refused service due to the age of my coach, the campground will not like my response on social media and I will gleefully leave the premises and move on to a more hospitable location.
While I am sympathetic with the squatter problem, there are hundreds of thousands of "Older RV's" still on the road and irritating this large portion of their clientele will not go well for any campground. The word will get out and they will find they will have no more campers thus no money. This change will occur rapidly with little impact on the campers as the number of camp sites is growing as are the various campsite sharing websites.
With that said, I am still in favor of purchasing a use RV at least for your first entry into the activity. Not only was it hard for me to figure out what I needed, what I needed changed over the years. As a close friend put it, If you purchase a used one and find out next week you made a mistake, you can sell it for almost what you paid for it and try again. With a new one you lose thousands of dollars when you drive off the lot.
This is the primary reason I recommend purchasing a carefully vetted used unit.
One last note, I am camped in a campground in Prince George, BC that has the rule. There are also numerous units as old as mine so the rule is selectively enforced at best.
My wife and I would travel full time, but we have to sleep occasionally.
2001 Tiffin Alegro Bus 40 ft DP named the Wild Eagle
Followed by the Eaglet - A 2005 Jeep Grand Cherokee.