There is some fundamental lack of confidence in these questions which I have never been able to fathom.
I agree with your incomprehension: it's difficult for me to understand children or teenagers, which is not a criticism of them, but rather of my own limitations as a pedagogue.
However, the question is still a pretty good one.
It's really been answered pretty well above, but I'll just give my own anecdote of one example.
Sure. When I'd begun studying seriously with a serious teacher, she decided that it would be acceptable for me to jump into grade 7/8 stuff after I'd demonstrated some acumen at interpreting simpler pieces of, say, Scriabin, Chopin, and Beethoven, in addition to my blues/ragtime background from a much younger age.
So, I was playing, and pretty well, 7/8-grade pieces, including for graded stage settings. We had to break down technical problems as they arose, which was simple things like the octave runs in the Op. 79 B minor rhapsody. And I played the Bach I wanted to as well.
It wasn't that I had no technique that I couldn't acquire at that modest level, as well as learning to work on pieces on my own, unsupervised, which I did constantly, it was that more abstract techniques like playing in double thirds or even single thirds in one hand were not part of the diet.
Mixed bag, really.
"Pearly" scales in all configurations, playing in thirds in the RH, things like that didn't get covered, except when they needed to for a few bars here and there. Not that easy to reinvent one's technique as one becomes accomplished in other areas of music, and as one's interests change over time.
However, the enthusiasm and dedication would surely not have happened in some kind of State-Sponsored Syllabus Academic style. I probably would have just switched to electric guitar and have been done with it altogether.
Yeah, it really is something that needs some consideration, and, most importantly, a complete decision about and committment to what one's priorities are.