As a kid, I never outlined anything. Maybe I’d write chapter summaries (that I never stuck to) and did character profiles (fun, and a good way to procrastinate) and some encyclopedia-like articles for planets & such (these are still fun), but I did not do what I would now consider “outlining”.
I never had to “outline” back then. When I was a preteen and teenager, I was full of ideas and writing was super easy. It wasn’t very good writing, and I often never got very far in any of my novels (especially before I started doing NaNoWriMo in 2008), but for the most part, I could sit down and write with no problem at all. I could easily work on three different novels a day and keep them all separate in my head with minimal notes written down.
For multiple reasons, this is next to impossible now that I am an adult. Not only do I have more responsibilities and a full-time job, but I also developed an autoimmune disorder halfway through university (which frequently gives me fatigue & brain fog). It’s difficult for me to keep track of things just in my head. Once I’m in the final plotting stages, I need to start writing things down or I will not remember them. An outline was optional in the past. It is now a necessity.
Since I’m frequently tired, emotionally and physically, it helps me a lot to have an outline to follow so I don’t have to do too much thinking on the fly. I have definitely seen advice saying to take days off and write when your health is better, but since my baseline is “mildly fatigued”, that advice doesn’t work. If I took off every day until I felt better, I’d never get anything done at all.
Also, the stories I write now are much more complex than the ones I wrote when I was a kid. If I don’t write down details, I won’t remember them. I need to make timelines to keep track of events, character profiles so I can keep track of characterization & backstory, location notes so I know where things are…
You get the point, I think. Things change.