I can estimate mine at 26k miles maybe? Not really sure TBH. The bigger trips we've take are easy to track because I kept all the mileage notes. However, that does not account for the "in state" trips to local parks, and two friends whom have farms that I'll take my RV for week-long trips.
I think a well-made RV can last a very long time if well cared for. My RV has a very high GVWR:unloaded ratio. It's rated at 7500 GVWR, but it only weighs about 4000 unloaded. Hence it has a very strong chassis that is has a lot of excess capacity. Even at it's max I've ever filled it to, it was only 5500 lbs, so there was still a 2000 lb margin of excess chassis capacity. That means there's less flexing at the loaded condition. Don't get me wrong, we want the RV to flex; if it were brittle it would snap like the Titanic. Some flexing is good; it gives rather than breaks. But flexing in a max condition means things are stressed to the limit (or very close to it). If you have a RV and you load it to the max, you are not likely to break it overnight, but you will stress all parts of it to a condition which can reduce it's lifespan. (Who would have though that class in material strengths would have been useful?).
RVs can hold up really well, or not well at all. It depends upon both the design and build quality. I would think your Airstream will do quite well; they are known for longevity.