In the Medieval world a young person of 7 was already an adult. As evidence he cites art work. There are no children. There are babies. But, what we call children do not exist.
Little adults are there.
The musculature, dress, expressions, and mannerisms are all adult. Consider how silly this well received argument was. The same artists had ample skill to paint adults, but they couldn't paint kids. Aries suggests another explanation, the one generally accepted today, namely that they couldn't paint young people as children because they were not children. In their cultures they were little adults, and this is precisely what the artists saw.