To make that much without a job, you need roughly $10M in the bank (yielding ~7% growth). That's a lot. A $500k/yr job w/o taxes or spending anything would take 20 years. The only way to get there is to have family money or hit the startup lotto (or actual lotto).
These articles are not about true economic freedom at 40, they're about limiting your consumption and being happy about it.