Selkirk exists in 2 varieties :
The hair can be REX (curly) or STRAIGHT.
Some Selkirks REX are told "homozygote" (understand " homozygote for the curly gene "): they inherited their curly gene from their 2 parents.
If the kitten inherited the curly gene just from one of his parent, so he is told "heterozygote".
Homozygote cats have a more angular look and less in curvatures than their heterozygous brothers; ears are bigger, eyes less round.
It's about 2 years that the Selkirk reaches his physical maturity. His hair as well as the density of its fur continue to develop up till this age.
To note: the seasons and the hormones (especially for females) play a role in the aspect of the fur, which can be more or less dense and curled.