That's not true at all. From 25/26 to now, he has kept his lifestyle the same (and improving).

He basically retired from his phd job, got super into finances, took a quant role for 70k a year, did that a few years, then he wrote his book.

His principles have stayed within him his life. The idea is to find things that are enjoyable as a hobby and then from there gain skills.

He gained enough skills and with his qualifications to get that finance job. But he did not have to work one day of it. He wanted to for the fun.

It is like in Skyrim, right. You might get all the gold, have god like powers, but there are still quests you can do for the story line (like the thieves guild or the dark brotherhood).