When do kittens start filling out?

My mittens is 5 months long and skinny. I was wondering when they start filling out and slow down growing? I know they can stop growing at 2 years but when do they slow down? Thank u everyone (:

Lol my Katsumi &Aiko are long &lanky. Eji is a little fat furball. I think its just how they are.

HappyLiz.  What are you giving him to eat? How much and how often?

Most kittens are rather round, although it is difficult to give absolute measures, they are individuals. it may also be because of lineage and possible breed-mix...

The growth use to slow down at 10-12 months. Although as you say,they can grow into 2 years, sometimes even more in some breeds/lineages.