This summer we have been spending much of our time in public RV parks. The is a switch from our usual trips which generally include more privately owned parks. For the 55+ crowd who motorhome you will find more people of that description in private parks as compared to publicly owned parks.
We stayed for a week near an awesome beach next to the cute town of Manzanita. This is a huge campground. Out of maybe 250-300 sites that were 95+% full the whole time were were there I did not see one other motorhome of 38’+. We were the only one. Even though this park has lots of spaces capable of fitting bigger rigs.
We enjoyed our stay here and will go back, but for those RV campers over 55 looking for other RVers of similar age and some commonality, this is not the best place for you. The average camper here was either in a tent or had a small towable. Most of the motorhomes were in the range of 25-30′. The average age was more like 30-35 for the adults. And there were lots and lots of kids. No sewers in the hookups either.
I like walking around the RV park with my dog and striking up conversations with people. In my opinion this is easier to do with people of a somewhat similar age to you.
Bob Nuttmann 
My husband and I prefer state and national parks for precisely the reason you outline. Nice to find your blog.
I made that comment after we stayed one week in a beautiful State park on the Oregon coast and then a week at a county park near Mr Rainier one after the other. This was mid summer and both were completely full. About 95% of the campers were under 55 and I preferred the next park which was a Thousand Trails park right on a river near Monroe WA. Very likely if we went now to either of those parks they would be uncrowded and quiet which is our preference. Nice to find your blog too. I was taking a close look at some of your pictures yesterday.