I have been painting on Yupo with oil paint. It seems to adhere well. Do you see any problems with using oil on Yupo? Also, do you think the layer of oil paint will protect the Yupo enough from UV rays that it won't yellow. If it does yellow - how much yellower does it get? I like using Yupo because I don't have to gesso it first.
If you don't recommend using Yupo with oil, is there a heavy weight paper that could be used with oil without guessing it first (which always makes it warp)?

Yes, YUPO is suitable for use with oil paint, and the surface requires no preparation. YUPO will yellow over time. DO NOT place the art work in direct sunlight OR expose it to florescent lighting without the protection of an ultraviolet shield. You may also want to try Arches Oil Paper, which also does not require gesso.

I have heard that oil on yupo will peal off after several years. Has anyone had that experience

Most oil paints will adhere to YUPO. However, as YUPO is a non-porous material, the oil paint will scratch off if a tool is used.

Here's a post by the artist SANDRINE PELISSIER that might interest you and answer some of your questions:

https://paintingdemos.com/painting-oil-n-yupo-paper/