Adjective order in academia: "Italian young adults"
I speak English only as a second language, and I don't do research that involves young adults, but my guess is that it's because "young adults" is a fixed expression that is very close to a compound word. So it feels weird to split it with an adjective. This would be a good question for English.SE, but I think that we are in the middle of a linguistic process where this expression is transitioning to become a true compound word.

Anyway, it is a common saying that "the international language of academia is broken English", so you shouldn't take academic texts as an example of style. For most academic writers English is a second (or third, fourth...) language, and many write by translating word-by-word constructs from their native language. It shouldn't be surprising to find the wrong word order.