I did not get my own laptop until I started at my university. I am now doing a Ph.D. in informatics (European meaning of the term). I had access to my dad's workstation at home, but just to play around on and I certainly did not have root or the ability to install my own software. There were computers in my computer lab at high school, but I rarely used them. They were locked down as much as any smartphone I have ever had.

At what age does someone need root access to become interested in a career in CS/IT/web dev/whatever?

Or, if not root access, like what kind of "desktop level capabilities" should I have had that I did not have, given that I did not have a desktop as a teenager or younger?

I am Gen X. I can think of exactly 0 friends who had their own desktops as teenagers. (Their own, as in were not really their parents' work computer, did not have to share with the family, could do whatever they wanted with, etc.)

I'm at the lower end of the millennial range and have personally experienced people who were a couple of years younger than me having to have folder hierarchies explained to them because they haven't encountered them before. This was in an introductory R course at the beginning of a master's degree at university.

https://www.theverge.com/22684730/students-file-folder-direc...

You do not need root access necessarily, but you do need to get familiarity with the platforms you will actually be using when working, ie. Windows and maybe macOS.

For Gen X and most of millennials, that platform was the only platform that existed. Using computers necessitated becoming familiar with "real" computers. That is no longer the case which is why gen Z are digital natives that have the digital literacy on a similar level to baby boomers.