Yes, it is not what I would call common but it is not uncommon either. Our previous coach, a 1991 Beaver Contessa, when we wanted to stay at the Outdoor Resort RV park in Las Vegas years ago, we had to send pictures of the coach before they would take/confirm out reservations. They told me with the owned sites they have to uphold the shareholders wishes to keep old run down rigs out of the park. I understood that as if I were in a $2M dollar Newell or Prevost sitting there I wouldn't necessarily want Cuzzin Eddy pulling in next to us.
However, once we sent them a couple of photographs we were welcomed in no problem, nor did we have any issue on any visit after that as they had us on record.
Portal RV in Moab has a very similar 10-years or newer policy in their south section, owners section, and since we have been going their regularly since the coach was only 4 years old, they allow us to continue using that section even though our coach is now past that ten year mark.
I have been asked about age from a few rv parks here and there but to be honest we have never been turned away. There are some that simply won't stay an any place that has such a policy and I respect that position as well, it is just that some of the parks we enjoy visiting do have an age policy.
Mike.