So it is absolutely and obviously not true that generational terms like 'millenial' and 'Gen-X' only apply to the USA, because the same characteristics apply (and are used) in all of Europe, most of Asia, Australia, New Zealand, South America, and so on.

Africa is a very big place, though, in varying stages of development. Several places have burgeoning middle classes, with access to similar amounts of consumer goods as the rest of the world. Is there any reason to think that these middle classes don't face similar generational shifts?