Does Anyone Know About ThreadyerStyle.com?

So I'm getting a Poreotics T-Shirt for my birthday but I'm scared the
sizes will be too big. I'm getting

http://www.threaderstyle.com/products/poreotoys-streetwear-black-t-shirt-/

What ages should get a small, what ages should a medium, and so on? If
I'm a 16 year old girl and my height is 5ft 5 what size should I get?
Thanks For Your Help! :)