I don't know what photo you are going by but in every photo I've seen she looks younger than her age. JMO. In the most recent photos she looks
just 13 but I wouldn't guess any older. She does not seem a mature 13 to me at all. She doesn't style her hair much or use lots of make-up. Her eyebrows are still natural. And she isn't wearing more adult clothing trying to look older. She doesn't try to make those pouty faces the older teens do to try to look sexy. She simply smiles a shy smile. There are not even any photos of Jayme that seem to be selfies-- all seem to have been taken by someone else. Although, you are free to disagree on perceived age or perceived maturity, I don't understand the point of debating it. She is actually 13 and just turned 13 in July-- 3 months ago. She is no where near the age of 15 or 16.
The above 3 are the most recent photos I believe (denim jacket was the Sunday before).
Observance, search planned for missing girl Jayme Closs
Some of these above are older photos (from when she was younger)-- sparkly outfits are dance costumes, not her everyday look.
https://i.dailymail.co.uk/1s/2018/10/18/02/5092458-6288639-image-a-14_1539826823179.jpg