Of all generational cohorts, older millennials are most likely to generate enough income to retire comfortably, according to the latest Vanguard Retirement Readiness report.
Specifically, millennials aged 37-41 have the greatest chance of landing a comfortable retirement.
You're getting at my favorite article of all time, The Shockingly Simple Math of Early Retirement. Say what you will about Mr. Money Mustache or even early retirement in general, but this article really is the absolute simplest and best way to think about retirement savings. It's why I often feel poor or pressed for money but never worry about retirement, because I max it all and pay myself first, and I know as long as my percentage is high I'm on track.
Plus even before I could max my 401k and Roth (and we recently had a kiddo so had to stop Roth for a bit) or get a high savings rate, I put in way more than was comfortable because the power of compounding is worth rice and beans and not going out drinking for a bit. Now that I'm middle aged my nest egg is huge, and we've been slowly able to lifestyle inflate. But I am soooo glad my younger self saved like crazy. Time flies by, and money compounds before you know it.