The Up Series[0]. It's a series that follows a group from children from age 7 through old age, and it's still going (in theory - the creator died last year). Seeing entire lives compressed into a few hours was very impactful to me.
Can’t upvote this enough. It’s fascinating what happens to each of the kids as some of them drop out of the series and then come back later. I hope it lives on past Michael Apted’s death in 2021.
[0]: https://www.amazon.com/The-Up-Series/dp/B074MGWDPF