Having a goal to retire at 55 carries with it some interesting sub-plots.
Anyone can retire at 55. The reason most don't is because they are afraid they'll have to give up something to do so, or are so wrapped up in the rat race that they can't see anything else. Or they just don't want to.
It also implies that the fun will start at 55. But what about all through your 20s, 30s and 40s? Those are the years we're most healthy and energetic. We deserve to have fun then too, don't we?
Life is a balance. If you wait to do everything "later", you're doomed. But yes, we can't throw tomorrow away for the sake of today either.
Simply saying that if you mange your money in a smart and conventional way, you'll be independently wealthy enough to live the great life beginning at 55, is a funny assumption. Yes, you'll be much more secure than if you didn't, but it also means you'll continue to live the same as the previous years when you were simply planning to retire. There is more to it and more to life and more satisfaction to be had early and later. If you never do anything but plan ahead, how will you know how to live at some time way in the future when your life has been dedicated to simply holding back and building a reserve and waiting?
Again, seeking a balance is the best course. Simply sitting at a desk and stressing at a job to build a fund leads to a heart attack. Working a physical job exposes us to more physical danger. Commuting, year after year is playing the lottery with traffic.
These are the good old days.