It depends on how many billions I have.
Obviously either way, my personal life wouldn't be different. I'd quit my job, never have to work again, have a house built from the ground up in an area thats as remote as possible without sacrificing good internet, buy all the anti-aging meds and supplements I want, get all the cosmetic surgery I want, fund research in anti-aging.
That's all I would do if I were a lesser billionaire. Now if I were a greater billionaire (have 50+ billion) then you're talking about an amount of money they could potentially change the world/society. My goal would be to advance anti-aging science and AI as much as possible. I would consult with some top researchers in these fields to figure out the most efficient way to do this.