ok, I have sort of done this just very recently.
At the age of 44/45, I quit my job to start a new profession. I have spent the last 3 years getting my license studying in my spare time, while saving a lot of money, as much as I could. BUT. after I quit, I ran into a road block, where I failed to get my website up and running, and then was not really keen on getting it started as I should, and am now on an extended vacation, etc. etc.
I have two kids, grades 10 and first year college next year. i presaved the college expenses, and I have passed most of the kid medical / therapy / etc surprise pain points. DH also had a serious illness for about 2 years thrown in there too.
I have a husband who has now worked about 2 years at a job that pays for 60 percent of our expenses, after being a SAHD (it happened unexpectedly when our second was a year old).
Take aways:
If you need the business income to make bank as planned in 2 years, you better have a steady but small and growing active income stream from it now. Too easy to put off too many of the start up details after you quit the day job, even if you have a lot more time.
There are many, many money and other surprises coming up for you with your kids / wife / her ability to work, etc. Pre-save enough for reducing stress later.
I missed a lot of my kids while they were growing up due to work work work, and I truly hated several years of it and my health proves that now.. hard to get it back after they go to college.
We spent a lot more money, foolishly, when the kids were up to age 8, because of that good money coming in. If only I could unspend some of my waste on those things. If you don't have the big income,because of a start up, you wont spend like that.
I am still able to spend the next 20 years working / not working as I like. I do have a lot of energy to travel and do what I want, even now. I have even started backpacking and gasp - exercising. I have enough saved to fire, if we downsize which is a great stress relief. No teslas for DH, however, in the near future.
So - mixed bag. It's life, not a guarantee.