Judging someones art ability from a very young age isn't a good analogy. I can't judge someones ability from words. I've seen parents/teachers rave about how good and "talented" some teens art is, but more often than not, they are mediocre in my eyes. Does that mean I think they can't improve? No, as long they are able to assess what they can improve on.

My art as a 6 year old was typical to other 6 year olds. Around when I was 11 is when I started taking the leap foward, learning shading. When I became 16, I developed the habit of the importance of having references and drawing more angular, and took a large leap in skills again. Doodles without references don't mean much, those are usually from only what you can remember. I think a lot of people who are bad artists simply don't know how to apply good practices, and/or won't bother to practice their weak points, as it is the boring part. Mastering the basics is the most important part to becoming a good artist.