We haven't run into any issues like that in state or national parks, but I have noticed several private campgrounds with age restrictions. We've only had one issue and that was with a private campground. The website made no mention of an age restriction, but after I made the reservation they called to confirm the age. They kept asking questions until they finally heard an answer they didn't like. We weren't allowed to camp there because our motorhome was too short. 🙄