Various. Different sources measure the generations differently. For one instance, some end Boomers in ’61, others in ’64. Then there is immigration projections. So there is more finesse in this than data people like. But trend wise, GenX just doesn’t have the numbers to stave off Millennials, and even at this last cycle’s peak, it wasn’t enough to get control of Boomers. Heck, team Jeb! went in with the idea that he didn’t need to be popular in the primary, he just had to outspend everybody. His team soaked up most of the GOP fundraising early on. Then they spent it and kept spending it long after it was obvious he wasn’t a viable candidate. Similar for Kasich at the end. They won’t yield the floor to new leadership, and we can’t push them away from the podium.
Or perhaps not politics? We had the same dynamic at church. If it is a leadership position that required nomination and vote, the 50 and 60 year olds had the numbers. The 40 year olds didn’t. Thus, some would fall away, going elsewhere, where their time and talent was wanted. The ones that finally busted into leadership had to be aggressive about it and/or required some affirmative action like policies. But I digress. You were asking about Boomers growth.
Yes, it is not GenX that will eclipse them, but Millennials. Gen X will still grow too, but not like Millennials. The basic cite I was thinking of was this from Pew: