I'm not talking about waiting until your 50's, I am saying that saving 33% of your gross income every year will NOT get you 10-15 years of your ending average of your last 10 years of earning, because your earnings are so much lower in your 20's and 30's. You would have to increase your savings rate in your 50's to 40-50% of your gross to get there.
I know, in that imaginary world where we all sat down in our 30's and figured out how much we would need to save each year, we imagined that what we saved in our 30's and 40's would actually GROW, not SHRINK, as it has for the last 15 years. We had scenarios where you had a return of 3-5% average each year. After the dot-com bomb and the real estate bomb (even though my funds weren't in tech or real estate), I've seen zero growth over the last 15 years.
I think it's wiser to do what our parents did, and to plan on seriously curtailing your expenses upon retirement - have your mortgage paid off, stop buying new cars, have budget travel plans.