Try government-run parks - no age discrimination.
State parks, state forests, national forests, national parks, county parks, etc.
I have a 1983 TT and a 2000 TV - never had any problems. In fact, I've gotten quite a few compliments on my rig. I would never stay in any of those snooty parks that discriminate.
Having said that, I have heard it said many times, that if you have a nice-looking rig, you can send them a photo via email or SMS, and sometimes they will make an exception. They are mainly trying to keep out ugly-looking hillbilly rigs and rigs that might break down on the property. If your's looks nice and is in good working condition, they might waive the age limit.