When are cats All Grown Up?

Mackerel is my first cat, and she seems to be growing very quickly. She's six months old, and we've had her for a month, and we think she's grown by almost half again in that time. So my question is:

How long do cats grow for? When are they considered 'grown up'? XD lol

typically 12-18 months thou if there is a bigger cat in her up to 4 yrs

Riley is almost 2 years old. He was six months when I got him and he doubled his weight since that time

I thought my Sasha was done growing but she grew until age 2.
I guess it depends on the cat.

Wow. XD 12-18-24 months?? Good God. Mack's the size of my friend's adult cats now, at 6 months.

It's not like they keep getting "taller" all that time though, at 10/12 months most cats are as "tall" as they get (I once read somewhere that most cats are 90% grown at 6 months, but I can't find that again). It is hard for me to find the words to explain it, at first they just shoot up until they kinda look like a gangly teenager, and then they mature into a cat with more normal proportions.

Maybe pics will illustrate what I'm trying to say:

Flynn at 10 months old, 5 kilos:



Flynn 3 years old, 4.8 kilos, he has not grown, actually lost a bit of babyfat, but his fysiology has changed from teenage cat to adult cat, you can't see it in this pic but he got a lot broader in the chest too (his eyecolor also changed a fair bit);

Mimosa, I get exactly what you mean. Thanks.

P.S. He's a handsome boy!