The word "millenials" as a classification is not used in China. Everyone gets classified instead as 80后，90后，00后， etc. (meaning born after 1980, born after 1990, born after 2000, etc.). Because of China's rapid economic growth, the difference in attitudes for someone born in the 80s versus someone born in the 90s is actually very pronounced.
I know nothing about China or how pronounced these differences are, but you see the same thing even in the "Millennial" generation everyone loves to talk about here in the US. You'll find a drastic difference between younger Millennials and older Millennials, to the point where Buzzfeed is writing articles comparing the two. No matter how much people want to pretend that "Millennial" is actually a real thing, it's not. It's entirely made up and the sub-generations inside of the category share very different cultural values and life experiences.
It's hard to argue that someone born in 1982 shares much (if anything) in common with someone born in 1998.
I think social scientists are now making a distinction between people who grew up with smartphone and without them. There are apparently quite large differences in behaviors and attitudes between these two groups of young people.
Compared to someone born in 1810, someone born in 2020 and 1950 have a lot in common. Compared to someone born in 1215, someone born in 2020 and 1810 have a lot in common. It still doesn't make much sense to lump them together and generalize their behaviors.
