I've always viewed employment as a spigot that you turn up or down as required to match the lifestyle you want. So depending on your definitions, you could say I "retired" from working 2000 hour years at around age 30.
I'd work maybe 3 months on a contract, save as much as possible, then head off traveling until funds ran low or I felt like working again (which was usually the deciding factor). I had a stint in my early 40s where I took a long term consulting gig and went heads down and did 4 day weeks for 4 years, so I guess if we're being pedantic we can say that moved the "retirement" age back to 45 before I downed tools completely.
In the meantime, I built a couple Software as a Service products that do their thing in the background and require pretty close to zero maintenance or customer support. That's the main income stream, though I still pick up consulting gigs on fun tech with fun teams as a sort of a hobby. Never more than a couple days a week though.
From this viewpoint, the bullet points up top don't make a lot of sense. I don't have $5M in the bank. I certainly couldn't imagine spending $150k in a single year, though I wouldn't consider anything about my lifestyle to be "austere". And of course I plan on making more "fun money" consulting. It's a fun job, and the people you do it with are fun to be around. It's just the part where they want you to do it 5 days a week every week that gets old. Never quit doing anything completely if you like doing it.
The two keys for me were consulting rather than W2 work, since that easily doubles your income while letting you jump in and out of work whenever you want, and the SaaS products, which keep a background income coming in when I don't feel like working.
Here's the long version of how I got into this position:
https://www.expatsoftware.com/articles/guy-on-the-beach-with...