Anecdote here: I was given a computer at age 4, and I didn't really have any limits on how long I could use it. On the other hand, I wasn't allowed to register any accounts and I had to ask before visiting sites I had never been to before. >75% of my time on the computer at that age was spent on hacking with Scratch. I learned a lot and developed my love of computers at that age. I'm absolutely glad that I didn't have "screen time", but I can also see that if I didn't have the limits I did I could have ended up pretty badly.