I was slightly confused when the video began. (Both by the level of detail a 9 year old kid could achieve and then the age of the "kid"!)
Edit: Since I've been called out as sexist, I should note that I apply this equally to women. I've likewise met 40-year-old girls and 17-year-old women, and the difference between them is the same: The capability to earn a stable income and take responsibility for themselves and others.
Sometimes being part of a partnership means you focus on internal rather than external roles: Supporting the family instead of earning an income. Who does what is then negotiable within the family, and that's OK.
We call women, with no stable income but devotes her life to her household, women. We don’t call them girls because ‘they don’t have a stable income’.
Assuming the article got his current age right, he was 16 when he started the model, and 19 when he started posting to Flickr (and amazing progress by then; most of the model was ready).
So I think it does qualify as a "kid". Maybe a more precise title would be "Artist started building a paper model of a Boeing jet when he was a teenager; took 9 years to finish", but I didn't feel deceived by the current title.
[1] https://www.flickr.com/photos/lucaiaconistewart/11782600196/...
'Kid' is baity too, but there are degrees.
A kid is, generally, younger than 13, though a 13 year old can sometimes be called a "kid". An 8-10 year old fits squarely in the "kid" bracket.