From the Drawing Development in Children link, 14-16yrs:

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The period of decision

Art at this stage of life is something to be done or left alone. Natural development will cease unless a conscious decision is made to improve drawing skills. Students are critically aware of the immaturity of their drawing and are easily discouraged.

I'm pretty sure I hit that "stage of life" by age 6. DD8 has already hit it, too. We're both highly V/S, which I think was the problem there, because the kind of results shown in all the stages up to 12 on that page are highly discouraging to us. The member of my household who truly enjoys art, and has produced remarkable works, is my DW. She's not nearly V/S to the degree DD and I are.