The count is less important than the buying power.

Millennials, as a group, have significantly less buying power than their Baby Boomer peers at the same point in their lives.

One source, but eye-opening if you can believe/trust the underlying data:

"Only a third of millennials own their own home, compared with almost two-thirds of baby boomers at the same age. It will take a millennial on average 19 years to save for a deposit, compared[0] with three years in the 1980s. A third of millennials will, it is predicted, have a lifetime of renting with less space, poorer conditions, longer commutes and more insecurity than the baby boomers experienced."[1]

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[0] https://www.resolutionfoundation.org/publications/home-impro...

[1] https://www.theguardian.com/society/2018/apr/29/millennials-....