Apologies for this being so wide.
Here I have an age chart for a monster that I considered to have a very "basic" looking design. :3 I have a somewhat lengthy explanation for his dramatic growth spurt in the middle, as well as his wardrobe updates in the last two.
Headcanon ahead! D8
This sort of demonstrates how I theorize a typical monster matures. It seems to me like they mature faster than humans in some respects - such as mobility and physical coordination, articulating and comprehending speech, etcetera - but mature at around the same rate in other areas like math, reading and writing, emotional maturity to an extent, and so on (although that last one can vary a bit).
I also imagine that they enter adolescence much earlier, given how some of the young monsters still learning to read and count are practically as big as their parents.
And because most monsters live alongside humans - most of whom can't always tell a "teenage" monster from an adult one on appearance or voice alone - those entering their "chronological teen" years and young adult years tend to start wearing certain types of clothes as a visual cue to non-monsters, as well as just signifying their new adult status. Not
all of them do, granted, but a good majority of them do. Anything from a simple shirt collar or pearl necklace to a full outfit can work.
So yeah, in my fanon, those such as Telly, Rosita, Murray, and even Cookie Monster, are biologically adolescents, but due to their overall mental and emotional maturity, coupled with their chronological age of 5-8 (at least, in my mind), they're still
socially considered children.
Thoughts? Even if you disagree, I'd like to hear someone else's perspective on this. C:
Also, I thought it made sense for Elmo's arms and hands to develop into the sort of bell shape that both his parents have. Still might tweek the design later, though.
... Good Lord, my text takes up more space than my actual artwork. OTL