I think the term yamadori implies that the tree is old. As in really old. Say, 100 years or more old.
Interestingly enough, I happen to own a JBP, about 100 years old, that was collected as a seedling in Japan. I wouldn’t call it yamadori. The fellow that collected it would go out into the woods each year and collect young seedlings, and bring them home and pot them. Eventually sell them as bonsai. Boon bought a dozen or so 25 years ago and brought them to the US. I got mine from another of his students.
Interestingly enough, I happen to own a JBP, about 100 years old, that was collected as a seedling in Japan. I wouldn’t call it yamadori. The fellow that collected it would go out into the woods each year and collect young seedlings, and bring them home and pot them. Eventually sell them as bonsai. Boon bought a dozen or so 25 years ago and brought them to the US. I got mine from another of his students.