An oil analysis is the only way to know if the oil life is done. Anything else is guessing. That said, I pulled a sample of mine after 4K miles (Valvoline VR-1 Racing 10w-30) and the TBN was at 6.3. And that was after 17 months. Anything above 1.0 is still considered acceptable.
The oil out of the bottle starts at 8.0 TBN (Virgin).
I'm now running Valvoline Full synthetic 10w-30
Any decent brand oil (even conventional) can live a long life 5,000+ miles. Age doesn't effect it so much as long as the engine is performing as it's designed to (no issues). RV's spend the majority of their time cruising on the highway at a steady speed. That type of driving is very easy on oil.
My recent trip I logged 3099 miles (US) and the oil has 5,527 miles on it. It was put in back in July 2020. I have no plan to change it until I approach 7,500 miles. I'm also using a Mobil 1 Extended Perf. filter