genx is now proto-boomer

Proto as a prefix means it's first or at least before.

I do not think that word means what you think it means. Proto boomer would be pre-boomer or at least the very early boomer, and chronologically that makes zero sense. Understand what you're trying to say though -- Quasi, Para, Pseudo, Demi would each be more appropriate prefixes. A Demiboomer could be in the Monster Manual.