That is completely unrealistic and impossible. They've never been immortal before, and they won't be until the end of time. It's undeniable that they'll have a lot of money to change and modernize the world to their liking, but I believe nothing lasts forever, and whatever they've created or changed will one day cease to exist. It's past time for people to realize that this world is just a passing fad; do what you can to achieve your goals and leave the world for the next generation to take over, and stop fantasizing about living here eternally.
Besides, even if they could fix their bodies to be healthy, they wouldn't want to fix their souls.
I'd be looking for a simple 2,000 or 3,000 years. After all, what is
in the face of eternity.