The audience here skews older and wealthier, so I suspect most would choose to be young again.
We'd go back in time? Do we get to pick the age? Suddenly being, say, 21 again but equipped with knowledge from a much later age would be challenging. For one thing, your cohorts from that time would suddenly seem immature. There'd be school subjects you've forgotten. That Differential Equations course would sound like gibberish, well, even more gibberish.
So, it might be better to pick an age of your first "real" j*b. OK, then you'd reach for your smartphone to look up an answer, and discover you have to travel to a library to use the card catalog to find information.
Quantum uncertainty means the future you remember will not be the one that transpires again. Buying Microsoft, Apple, etc. stock seems like a lock to FIRE, except your knowledge of the future will leak out, perhaps causing some other company to be the one to create the killer product. Predictions are hard, especially about the future.