At least, everything we've ever experienced, county, state, and federal camp grounds don't have age limits. Every county, state, or federal campground we've ever stayed at also allowed tent camping, pick-up truck campers, and pop-up camping. We've never run into any private campgrounds either that had an age restriction rule. But, we very seldom do private campgrounds, with the exception of KOA and Good Sam campgrounds, which I've never seen an age restriction there either.
I have hard of some RV "resorts" folks have talked about on these forums that do have age restrictions. But personally, I'd never stay in a "resort". There are some "resorts" that are restricted to CLASS-A motor homes also.
I think your friend, traveling for employment, probably bumped into a section of the country that does have age restrictions, primarily to keep keep a trash-city being created with a bunch of transient employees. Local jurisdictions may also put restrictions on certain areas in order to keep the "junk" and ash-and-trash out. Age restriction is one way to do that, and can be enforced without any kind of prejudice. It's a rule, it can be enforced, and since it's a private organization, they can do whatever they want. This is the #1 reason why we select county, state and federal campgrounds. Their "restrictions" are usually the number of days you can stay and then you have to leave (usually 14), then can return after 3 days again for another 14. This keeps campgrounds accessible for the public (as they should be) if they are county, state, or federal. It keeps people from settling long-term and taking up permanent residence, like a lot of work-campers have a tendency to do. (They stay for months at a time) making it impossible for local residence to camp there.
So yes, the age restriction campgrounds are out there. But they are far between, depending upon where you live. I understand it it is more common in higher residential areas and city areas, but never hard of it with county, state, or federal parks.
