1997 Class C Winnebago, 47,000 miles too old to buy?

is there a rule of thumb that says RVs shouldn’t be older than

As said, very good inspection then weigh to cost difference of repair over a newer unit. Personally I would prefer a newer 6 speed tranny over a 4 speed.

It also will depend on where it was stored. If it was in a dry climate that's a good thing. If it sat next to a boat ramp or was on an oceanfront lot of a beach club then I would pass on it.
You would probably also pass on it too when you attempted to move it and the wheels feel off. Regarding the chassis I think rust and corrosion will be the enemy to inspect.
Regarding the coach, it will be the caulking and how it was maintained over its life. Water intrusion will seeks the lowest level to settle and follow gravity using the framework as roadways. If you have water damage in the drivers side rear, the leak might have originated on the passenger front side. Floors and such should feel solid not spongy, check the floor at the entrance door. Rv doors are notorious leakers.

sounds like a great barn find. this one should have a rv inspection. coat a little but you,ll learn more in his report than you could find. one thing,IF theres water stains ????? run. mines a 2007 and we load it and drive it to AZ all the times. this winne will need new belts hoses oil etc before you go 10 miles, tires will be your big chunk of money no cheap tires michelins for me. nothing kills a trip like a tire blow out.have fun and when something does break laugh it off/

If it is well cared for, good mechanical and rv systems condition and un-molested (i.e., not full of hack repairs), it should be a very serviceable unit. And a great value at that.
Again, the miles are super low and that is a bonus, but don't falsely believe that the chassis and drivetrain will be totally relaible as if it was 3 years old and driven 15k a year.
i would have no issue with it, but my view is that I can/will repair most anything save for rebuilding the engine or trans as it comes up.
Realize even "simple" repairs are expensive if you're paying someone or a tow bill.
Are you comfortable with major pre emptive maint/repairs before you embark, or potentially fixing cooling system or brakes or ..... For example? Or is it a tow truck to the nearest shop and a repair bill for you?

At a minimum, all fluids, hoses, belts, tune up, newer tires etc "should" be done to minimize the chance of the "little" stuff breaking down. Budget for that.
Not trying to be pessimistic but that's what you need to prepare for with an old rig. It's not a certainty, but you dunno until it happens.

The RV portion on the other hand is less of a concern, IMO. Most repairs are fairly basic. And aside from losing the fridge, for example, can be worked around with relative ease. (You can figure it out for a few days if say the water pump dies or heater don't work, unlike breaking a fan belt on the rig and being out of commission on the side of the road without the knowledge or parts to fix)

IMO, the nicest 23 year old class C out there is worth maybe $10k tops, budgeting for making it reliable.

I know this sounds negative, but it's how I'd view it having good knowledge of mechanics, and kind of a prepare for the worst and then you won't be disappointed and likely have a better experience.

Twenty-three years old and cross country...I wouldn’t.

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

Thanks for so much for the answer. It makes a lot of sense.
It is exactly how I approach it as far as “in case the RV dies”... at least we didn’t bury ourselves in debts.

In my opinion, no, it's not too old, especially for a first-timer. Definitely do your full due diligence, and get a good thorough inspection, but expect the inspector to find a good number of issues (as with a home inspection) -- then you would have to decide which of the issues are worth spending money to fix, and if the purchase makes sense at that point. 47K is nothing, assuming it was used regularly and hasn't sat idle for an extended period of time (47K on a '97 is only an average of a little over 2000 miles per year). Also, the unit you describe is probably no more than a $12 - 15,000 motorhome, so if you bought it and ended up hating it, you surely wouldn't face a huge loss re-selling it as you would on a much newer unit. The only drawback is if you ran into one of those snooty campgrounds that doesn't allow units over 10 years old, but you probably don't want to stay there anyway! Good luck to you!