My question is what is Gen Y??

I just googled it & got:
1) 1981 or later
2) 1977 - 1997
3) 1976 - 1985
4) 1980 - 1990

This article is referring to 18-29 year olds, so 1980-1992, I wonder if another article on Gen Y using a different definition would get a different result? Just thinking out loud...