Most of that info is spot on actually. If everyone followed the simple advice of saving AT LEAST 12-15% beginning when they got their first job, they would be all set for life and could probably retire in their 50's without a problem. It isn't FIRE by this sites standards, but it isn't bad advice, and better then a lot I have seen on other websites.
No. The math says a 12% savings rate will take you 47.5 years to become FI at a 4% SWR (and that's if you start at 0 net worth, many people start negative).. assuming you begin work at 22, out of college, that puts you FI at age 70 or so. 15% puts you FI around age 65 given the same premises.
20% gives you age 59. You have to go all the way up to 25% savings rate to ER at age 54. So a 12-15% won't get you FI before you're done working and eligible for SSI. One has to hit the 25% rate to FIRE in their 50s (and must do it year in and year out, and be starting at 0). Once you ramp above that (50%, 70%) it really starts to accelerate, but the conventional wisdom will get you a nice nest egg at a normal retirement age, and that's it. It won't let you FIRE in your 50s, as you say.
(Unless you assume other things not mentioned, like never inflating lifestyle/banking all raises, or something.. but just saying 12-15% consistently won't ever get you FIRE'd before your 60s.)
I think the advice to save x% is total garbage, and I wish I had someone like MMM to mentor me when I was younger. The entire premise behind conventional thinking is to work a fixed number of years and inflate your life style to match your earnings, which I think is fucked up and ass backwards.
Agreed. So much money is wasted because people just don't think about it, and don't know any better.