Allow me to say approximately the same thing in a different way. Adam, I guess you would agree that there are some people who will almost certainly never found a really successful startup no matter how often they try. Do you really think Pr(you are such a person) is less than 0.1%?

Further:

• I think it's more like 75% of startups that fail.
• If you have no savings to speak of, then after a startup fails you will need to go back to "ordinary" work for a bit to raise enough money to start the next one.
• You may find it harder to raise investments if you have a few failures and no successes under your belt. (Again, if you have no savings to speak of you will need investment quickly.)
• Mean time to failure may be only 2 years, but (a) I suspect that the most likely path to startup success goes through startup near-success, and (b) nearly-successful startups probably take longer to fail, and (c) actually-successful startups typically take well over 2 years before they start delivering serious money.
• A startup that doesn't fail doesn't necessarily make you rich. You probably need quite a big success for that.

Let's suppose you don't care about (c) above because once you've got a successful startup you don't mind waiting, so your 20-year window indicates only how long you have to start an eventually-successful startup. Then in view of the numbers above I suggest an optimistic timeline looks like: some number of iterations of (1 year working to raise money, then 2 years for a startup to fail), then one of (1 year working to raise money, then 5 years for a startup to only-just-fail), then one of (1 year working to raise money, then startup succeeds). Then you have time for about 3 "quick" failures and one "slow" failure before succeeding. At a 75% failure rate, that's a lot less than a 99.9% chance of success. And if you fail on this path, you're now fortysomething, you have a long track record of failures, and you have no retirement savings at all. Good luck!

(When I say "an optimistic timeline", of course I'm aware that some people get there much quicker. But you have no reason to think you're in the lucky not-very-many-percent who will succeed first or second time around.)