I got Perry around 8 months and he was mostly at his current height (though I didn't measure so not positive but very close) BUT he did fill out and gained 2 more pounds. I remember because he was around 9 pounds when I got him and the rescue said that if he got much heavier he would be fat (they were wrong) but he's now at 11 pounds which my vet and I agree is the right weight for him... when he falls below that she (the vet) does comment that I need to feed him a little more
I can still use the harnesses that I got for him at that point so I know he didn't grow very much more after that

. (I mostly have to adjust the harnesses for how furry he is rather than actual weight)