Math is math.
Savings rate doesn't care if you are 22, or 50.
When you're younger, you have time on your side for compound interest, but one of the awesome things about the MMM high savings rate strategy is that it minimizes your time of working/saving, so the compounding effect doesn't matter much.
When investing a small amount for a long period, yes, there's a big difference between 20, 30, 40 years.. but almost all the gains are over those last few years, from compounding. When investing a large amount for a short period, almost all the money is from savings, very little from compounding. So being older is just fine.
At the end of the day, it's numbers. It's math.
Saying "this is gen y" or "what about boomers" or whatever is irrelevant. Labels in this case aren't just useless, but actively harmful. Optimize your spending, save as much as possible. Then go enjoy yourself, both before and after FIRE.
:)