Republican and conservative are not identical terms. Boomers are not a majority Republican, but they are a majority conservative. (Actually it’s a plurality, not a majority, so I did misspeak. It’s a very hefty plurality, though.) Conservative Democrats are a minority in the Democrat party, but they exist, and they help pass conservative legislation, and they block progressive legislation.
Also, as of the 2016 election, boomers still outnumbered millennials, but maybe that’s changed. I haven’t heard the news if it has. The trend line for boomers is going to accelerate down as boomers become older. You also have to factor that around 70% of boomers vote whereas only about 50% of millennials vote.
Also, where was I scapegoating boomers? I said they’re consistently conservative. That doesn’t mean they deserve to be homeless or each one is personally responsible for the housing crisis. I think you might be assuming that everyone younger than the boomers is a monolith.