>Maturity here simply refers to the emotional maturity of a person.
I didn't think of it as a perception of a purely physical quality (head, eyes, legs, etc.) but as a perception of the whole of a person (thus a perception of how one bears oneself).
What we think of as mature and what people generally mean by mature are two different things. It's not that I think the qualities considered "mature" here are negative but that to call them "mature" leads to misconceptions about what people usually mean by maturity and immaturity.
For everyone that isn't oneself, appearance is reality: what we see of a person is that person to us. We may suspect other qualities within a person, perhaps prying into their actions hoping to discover something about them, but these qualities are purely imaginary until shown by action to be true. Even then, I suppose, they're still imaginary--only impressions of who a person is rather than the substance.
Maturity is just one of many impressions. To say "this is maturity" when it contains only imperfect aspects of what might or might not lead to that perception detaches the word from its context, resulting only in folly. It's probably the work of someone who, like many of us, lives on the internet where the qualities called "mature" in the image are somewhat more likely to afford a person that title (although even that is not necessarily true).