I'm not the person you asked but I also am a very fast home cook due to professional cooking background.
The job is the training in that kind of work. No one comes out of culinary school particularly fast and even most serious cooks don't go anyway. Cooks change restaurant often and every restaurant is a completely different set of foods and techniques.
Training may teach you how to do something but doing it for hours a day months straight is where you learn to do it fast. A skilled cook at the prep table is looking at it like an F1 pit crew basically. What physical motions am I about to perform, what can be set up in advance and where should it go to reduce extraneous movement, what are the intermediate steps that can be batched together etc. There's never enough time for all the work you need to get done in the kitchen, so every day is a challenge to optimize your efficiency more than the previous one.
Basically you can teach someone the right way to dice an onion but they won't be truly fast at it until they've diced a few thousand onions. Apply that to every task in the kitchen over a decade and you're pretty quick by the end of it.
Even just some deliberative practice for a home cook can make a big difference. I am absolutely, positively not in the professional league. I'd be drummed out of any professional kitchen in the first five minutes. But I'm also way faster, better, more able to recover and improvise than I was twenty years ago, because I deliberately tried to stretch my skills a bit. Not a lot. Just a bit every so often. Over 20+ years it adds up.
It's just like any other intricate physical skill that requires practice, like music or sports.
I've started seriously learning guitar / ukulele, and it's amazing what improvements you can get just spending a few minutes a day where you slow down, do drills (like practicing scales), and analyze what you're doing.
The first time I play a new, unfamiliar piece of music with any tricky bits it feels awful, and I hate it with every fiber of my being. I want to run away and give up on ever learning it. That's when I take a break and come back the next day - when it usually seems much more accessible after I've had time to process it.
The first time you practice cutting an onion the "right" way will feel really slow, annoying, and taxing to your brain. You'll want to do it the way you're used to, even if that's horrendously slow. Do this every day for a week or two and you'll be amazed that it just happens naturally without having to think about it.
Yes for sure. And professional cooks are focused on different things too, not all of their skills are normally applicable in home cooking. The two best cooks I know (both better than me in terms of consistently delicious food) are as you describe: older people who have just been paying attention and caring about it for a long time.
