For anybody, I’d generally say at death. Even later in life you can still pick up at least some interesting hobbies, which will also help you find friends. I know a lot of people in ham radio and postage stamp collecting are older, already retired, yet they also attract young people.
Sure, learning may get harder, but the amount of free time will compensate for it.
You’re still a person, no matter if you’re 10, 20, 50, 80,… and you’re not the only one. So life just ends with death.
Myself? I don’t know. I can’t encourage myself. It feels like I am late to anything. I never dated, yet most people I know did so in middle school already. I didn’t yet learn any programming, yet I know people who did so since they were 13. One of my teachers was already fixing computers for others for money when he was just 10. I know someone who got CCNA certification mid high school. I know one 16 year old who seems to just know everything related to networking and self-hosting.
Meanwhile I only got my first proper computer when I was 14 and barely knew the concept of operating system. In 2 days I finally got Linux Mint installed on it, but I didn’t even know what a partition is.
It just feels like I am dumb and late to absolutely anything at this point.
Since I’ve spent like the past 1-2 years spiralling down into these thoughts, for myself I’d say 16-17 (I am 18 now). I just wish to be dead.
But if you’re asking because you feel like your life already ended, I am pretty sure you can still get back. You’re definitely not the only one feeling like that, and that alone already unites you with a bunch of people.