> I'm full stack for 19 years

That's the key.

I've been an AppSec engineer for about 12 years, but it wasn't until about 5 years ago I started working somewhere that actually paid a market rate. I wasn't living paycheck to paycheck for the first 7 years, but certainly wasn't putting much away.

Now, I've got nearly a full year of after-tax paychecks in savings. I could easily go ~18 months without pay without a change in lifestyle. I could stretch it out to 3 years with some belt tightening.

In about 6 more years, the house will be paid off and any savings I have could last even longer.

Presumably they haven't been living paycheck to paycheck for the past 19. It's not that difficult for a SWE in North America.