As someone who knows quite a few billionaires- they have a habit (lots of multi millionaires do this too by the way)that middle class people don’t generally know about… the answer is…

They spend as much money as possible on physical and mental health. I’m speaking about making sure to work out their brains via extra cognitive testing, and teasers (like doing a super set for the brain) they also spend hundreds of thousands if not millions (or tens of millions) on sculpting their bodies via trainers, nutritionists, and maybe a few elective surgeries. Two examples you can look at are Jeff Bezos and Elon Musk. If you look at them 20+ years ago compared to now, whats different? One, they look better in a physically attractive way, and secondly, they are more fit and act younger than they did before.

The not so secret for millionaires and billionaires is you cant buy immortality, but, you can make your life more worth living, and tentatively increase your longevity. Sometimes (not all the time) the average diet of a billionaire contains less harmful items in the food, than any other group. All the time, these billionaires have had, or still do have personal trainers that would look like the ones that made Kumail Nanjani (now to be in the avengers) look like an entry level personal trainer.