Check out https://ficalc.app - using your numbers, you have a 96% chance of not running out of money (assuming bitcoin grows at normal market rates). So, yeah, I think it's doable with your numbers.

The only thing I might worry about is that ficalc shows that starting your retirement prior to a rough economy lowers your chances of success. Since it feels like we're heading for a recession/deprecation or stagflation I'd be worried to start "retirement" now. I'd want to wait until the economy felt like it was coming back or until bitcoin decoupled from the market. That being said, a 4% chance of failure is pretty darn small.

Of course, ficalc assumes your stack grows at normal market rates. It doesn't take into account the fact that bitcoin has tended to grow 150-200% each year (over 10+ years). If bitcoin continues to grow at insane rates then 21 might make you insanely rich and you might decide to move to a high cost of living country. :)

I'm with you, though, I tend to believe that around 21 bitcoin might be all a person needs. But, even if I had that amount, I wouldn't feel comfortable "retiring" right now. Maybe when the SMA1458 (https://charts.bitbo.io/sma1458/) is at around $100k at today's dollar... Just gotta keep stacking before it gets to that rate.