Recently changed the CVT fluid on my 2011 Nissan Altima 3.5SR, 42k miles on the fluid, 90k miles on vehicle. Possibly worth noting is that the fluid was in there 8.5 years, as I only drive this one about 5k miles/year. I surmise that the age of fluid is much less of a factor on fluid breakdown...
I'm considering a 2018 Hyundai Tucson with the Nu 2.0L GDI engine. There is a well-known history of the Theta II engines having catastrophic engine failure well before 100k miles. It actually led to a huge class action lawsuit and settlement. Since that engine has been used in some trim levels...