Birth: Summer 1979 (Disco Demolition Night)
Rising years: 1980-1982
Main years: 1983-1995
Echoing years: 1996-1998
Death: ~late 1998 or early-mid 1999 (teen pop becoming more popular as the 98-99 school year goes on)

I would make an argument that 1989 is probably the peak year of Generation X's pop cultural age. The Fall of the Berlin Wall took place, glam metal starts declining, and some artists who would set up the tone for how the core 90's would look like started making some material that year (like how Nirvana released Bleach for example).

I disagree that Disco Demolition Night marked the "birth" of Gen X culture. The oldest Gen Xers would have only been 14 years old at the time and people of all demographics took part in the event, not just people who were born after 1964. As cliche as it sounds, I would personally consider the launch of MTV to be the "birth" of Generation X culture. 1980 and 1981 were still predominantly Boomer cultural years.

I would say 1991 because not only was 80s MTV culture still going strong at that point, it was simultaneously when Nirvana became famous and gangsta rap had grown popular in non-commercial hip hop circles.