No, there is no rule of thumb. Many of us have older RV's.
CONDITION, is the important factor. If you are not familiar with RV's hire a mobile RV Tech and a qualified mechanic to do a prepurchase inspection.
Leaks are a killer of any RV. And, if you don't know, RV tires age out before they wear out. Factor in the cost of a set of tires when making an offer.
The roof condition is another consideration. It may need coated or replaced.
Do not give the seller, dealer or private, any money or sign anything until you are satisfied with the condition of the unit.
You're doing it right by asking questions before you make a purchase.
Don't hesitate to ask lots of questions on the forum, someone will have the answer.
Use your search as a learning experience
