I have a cousin 7 years old, but still resemble 4, the child of 5 is same, what is this to ask?

I have a cousin, this year 7 years old, but still resemble 4, the child of 5 is same, I look say on a book, some dot, development is gotten early, the evening of some development, some dot 7 years old..
http://medicine.gegemeimei.com/internal_medicine/t17709