I just looked that up and apparently there are 10 or 15 year rules enforced by some but not all parks. If the RV is older than 10 or 15 years it will be barred from entry.
Apparently the rule is to deter people who do not maintain their clunker of an RV which might break down, leak various fluids or catch fire. The given advice is to keep your rig in good shape and call the RV park and explain the situation. They may request pictures as proof e.g. a well maintained conversion of an old city bus would be fine if your pictures show as much. Some parks might inspect on arrival.
Have dealt with this. I own a 2007 RV. Maintain it well enough that it isn't an eyesore, but I'm not going to waste my life on upkeep. I have never been turned away from an RV park in the last ~6 years that I've owned it, even when staying at "must be 10 years old or newer" camp sites.
Like you said, it's more used as a policy to turn away. People who the park doesn't think fits their vibe.
New dream policy for California: no more 20+ year old RVs street parked in touristy places. They'll end up taking over entire streets around mission bay (a large park in San Diego)
Apparently the rule is to deter people who do not maintain their clunker of an RV which might break down, leak various fluids or catch fire. The given advice is to keep your rig in good shape and call the RV park and explain the situation. They may request pictures as proof e.g. a well maintained conversion of an old city bus would be fine if your pictures show as much. Some parks might inspect on arrival.