My family got our first computer when I was in the second grade. It was for video games and basic programing, so my first typed pieces were on a green travel typewriter.
By the time I was in middle school we had a computer with a printer and word processing programs to type up papers. But research and rough drafts, worked on in class, were handwritten, usually with highly specific methods (note cards, graphic organizers, 'double spaced' rough drafts) according to the individual teacher.
I was in high school before I truly started from a blank computer screen, coming up with the words as I went, then editing on screen.
It's a different sort of process. For one thing, there's no real need to start with a first line and go in a particular order. It's easy enough to start in the middle and rearrange as needed. No pressure to spend hours getting your first line perfect before going on to the next three hundred.
Not everything is perfect. There's that whole distraction of the internet, or even if you turn that off, the choice of fonts and a hundred other formatting decisions.
Whenever I cannot think about what to write next, I hit the enter key. I won't realize sometimes just how many times I have hit it, until a fifty-word post takes up a full screen. Sometimes I remember to go back and edit. Other times I do not.
(I still proofread from a printed copy. And yes, my default is two spaces after a period. I'm working on it.)