I’d like to be able to make almost anything by hand that people could. I’d like to be able to knap flint knives and axes, start a fire with nothing but a hand spindle, tan animal hides and furs, make and hunt with a bow and arrows. Then be able to build a blacksmith’s forge starting from nothing but raw materials. Be a carpenter, a potter, a glassblower, a weaver. Reproduce the start of the Industrial Revolution by starting at the mill and lathe level. Make a flintlock rifle by hand. Grind and polish lenses for a telescope and a microscope. Recreate practical chemistry. Build a clock. Maybe a printing press. In other words, be a polymath artisan; a cross between Galileo and MacGyver.
Maybe I could finally get the garage cleaned out.
Are we assuming we learn at a rate common to adults? Because there’s a big difference between learning at an early age and learning later in life. I’ll assume we are young adults when our extended life begins - fully developed and at our physical best. But it still won’t be the same as learning something as a kid, especially when it comes to things like languages. So for me:
- Languages, at least three or four
- Lots of physical skills - I’ll put in the time to qualify for major league baseball no matter how long it takes
- There are a lot of airplanes I’d like to try out. Which reminds me… are we actually immortal and protected from accidents?
- I’d like to learn a lot more about math and chemistry
- Ragtime piano
- And I’d like to be able to whistle really loud. I’ve read tutorials and tried several times, but it never works. I think my mouth or tongue are just the wrong shape.
This^^. Being a polymath at everything sounds great. If sorta-immortality strikes at age 25.
But if I have an extra thousand years starting now as lazy retired me, I fear it’ll mostly be spent in the pursuit of ever greater hedonism. That’s certainly my current trend and it’s very nice.
I’ve often fantasized about this, like the protagonist in the first Highlander movie (the only one that exists, of course), or Corwin from the Chronicles of Amber fantasy series by Zelazny.
Anyway, I’ve always been interested in lots of different things. I would use the time to become an expert in lots of different fields. I would go to medical school and become a physician, and get pilot training, and get degrees in every field of science and engineering. Then start branching out into other fields. I would learn multiple languages. I would read a lot.
And I would travel. And partake in every form of recreation imaginable, from skiing to scuba diving.
And it goes without saying that with time I would be very, very rich. Not for its own sake, but to afford all of these hobbies.
But then again, maybe I would just waste all that time, kind of like I’m doing right now. I think the only way to make the most of your time on this Earth, whether it’s 80 years or hundreds of years, is to tell yourself that time is short.
I’d do something to achieve my longtime never-achievable dream of being a movie director. Of course, who knows if centuries or millennia from now if movies are even still around.
P.S. It occurred to me after writing this that I should have included something about using all that time for philanthropy or to do good works, but I fear it will come off like Steve Martin’s Holiday Wish. 
Make a to-do list.
Mastery of the piano and the guitar. Mastery of chess. Mastery of at least one, maybe multiple martial arts. Mastery of Spanish, Italian, maybe German. Mastery of sourcing and/or foraging the freshest, seasonal ingredients, and mastery of cooking them in a variety of styles.
Assuming age 25 as ideal continuity …achieve competency in what happens to catch my whimsy…..don’t really need mastery as that implies more dedicated effort than my mindset is usually comfortable with.
Mind you I got my solo pilots liceence in 6 weeks and I would love to fly sailplanes in more locations so I CAN push but prefer not too….rather to sample an interest.
Enjoy riding the upcoming eMotorcycles in a variety of locations as the silent speed would be a great enjoyment.
And to know the inevitable age decline I’m suffering now is avoided for a good while.
Oh yes, learning to fly an aircraft, I forgot that. Assuming I had the requisite money, I’d get licensed to fly every type of private aircraft (single engine, twin engine, jet, turboprop, yada yada) in all conditions (VFR, IFR, whatever others there are).
I think that’s a point very often missed about immortality/longevity. If you have a virtually limitless number of days ahead of you, the opportunity cost of wasting any given one tends to zero. Why start today? You’ll have lost literally nothing by starting tomorrow, thus any given amount of inertia and satisfaction of more immediat needs would be sufficient to endlessly defer any pursuit. Whereas with a finite lifespan, the choices you do take matter, at least in part, for the options they close off: if I train to be a mechanic, I’ll probably never become a concert pianist—but with limitless time, no such conflicts arise. At the bottom, you could do everything, but never have any reason to do anything.
I’d have a lot of kids, would they be near immortal as well? Or would I have to watch them grow old and die? I don’t think that I’d like part very much.
Well you cetainly have the money to learn to fly a sailplane even now. Usually about $3k r covers your training and 40 short flights you need to become a licenced pilot.
There are clubs all over. You will have some volunteer work to do for the club in return. I find flying motorized aircraft quite boring as opposed to sailplanes.
Many commercial pilots also fly sailplanes for fun as opposed to the boredom of driving a bus in sky.
I’d do a lot more traveling, for one thing. There is much more of the world than can be seen in one lifetime.
Then, alternative careers. I have often thought that in another life I could happily have been a professional music engineer / producer. Or a professor of chemistry at a good university.
I’d take up slumbering. It works for vampires and ancient eldritch gods.
I’d do a lot more traveling. Like, spend a few centuries building and then using a Generation Ship, as we’ve discussed in other threads, but without the need for “generations”, which always seem to be where these things go wrong in sci-fi stories. Make it big enough and populous enough not to get bored while you’re en route, that would be the key. I figure most people spend about 90% of their time in the same one city anyways, so it can’t be that hard to make a city in space that would keep you occupied.
One thing I WOULDN’T do is form a lot of close personal relations. As another poster alluded to above, watching everyone you love grow old and die would be a serious downer. I suspect I would get a little lonely and pensive over the course of a thousand plus years.
I don’t have many ambitions. If I had centuries of millennia to live I would work long enough to build a nest egg that could support me virtually forever because the growth rate was higher than the amount I pulled out each year (probably 2 million or so in principal). After that I’d never need to work for a living again.
Then I would just enjoy as much media as possible. I’d explore different kinds of music, TV, film, books. I’d learn as much as I could about subjects I enjoy and I’d wait to see how AI unfolds.
There have been quite a few SF tales about this. ‘Time enough for Love’ by RAH, for example.
Then there is ‘Grotto of the Dancing Deer’ by Clifford Simak.