Wow! That's a tough one!
You can easily find short guided tours in popular destinations. However guided tours over several days are not very popular in the U.S. compared to other countries. And camping tours seem to be even less popular, particularly among seniors.
When searching online, I found many camping tours in Africa, Asia and your home country. Finding something in North America was much tougher.
This site is run by some Brits. Their description states that they do offer 50+ itineraries. During the short time I spent on their site, I did not find tours specifically for the over 50 age group. But I think that they could be a helpful resource. The main thing is that they do offer Camping Tours of the US.
http://www.trekamerica.com/Tour_Search/adventure_search.html
This site lists Senior Groups in their description. Again, did not find any tours specifically for an older group. So you may need to contact them to inquire. But again, they do offer camping tours.
http://www.camping-trips.us/
Good luck!
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