I've had mine since 2005, and if I decide it fits my needs as I get older alone, I might keep it another 10-15 years. Or I might give it to my kids to use and get something entirely different, like a tiny TT or a pop-up. Then they might use it for another 5-10 years, or maybe not, as their kids grow up and leave the nest. More on that later.
I've seen very few RVs traded, sold, or abandoned because they were worn out or no longer useful. There are hundreds of 1970s Winnebagoes running around out there, saw three on the road today and a half-dozen more parked as I crossed Indiana from the Elkhart area toward Champaign-Urbana in Illinois.
RVs get traded, sold, or abandoned because the needs (or more often, wants) of the original owners change. Almost every RV that gets sold because it is "too old" very shortly becomes someone else's "new to me RV" which may be kept and used much longer than the first owner used it.
I think the risk you face going into retirement with a C you bought now is that it may fit well the way you use a RV now, but when you retire the way you use a RV will change, and something else, maybe a larger A or a fiver, may be more useful.
Wife and I got our 30-foot C to use for travel, and for a one week each month group "campout." We used it that way, traveling 30,000 miles over three years, the two of us and some trips with 3-4 children and grandchildren. Then she got sick, and our travel became trips to the cancer center, and the RV got used only for the group campouts and one more long trip with the kids.
Then the camping group started dying off (five members over three years, counting my wife) and there is not much left of the group that camps, I need to find a new group. Alone, I don't use the C for travel, it is a lot more RV than I need, I'll be outfitting a van as an overnight camper. The C sort of works for solo trips to one of the lakes for some quiet time, but it is big, I have to tow a car to get around while the C is parked at a lake, think I'd get better use out of smaller towable.
Every one in our RV club, most now in 80s and RVing or camping for 30 to 50 years, is on 3rd, 4th, etc RV, because over the years, from starting as a couple, raising growing families, having kids grow up, changing from vacation or travel use to more frequent and longer uses, meant getting rid of one RV and moving on to something different (not another of the same).
That's why any particular RV might not be owned for a long time by any single person, though it might be owned for a long time by several people in succession.