At only 1yr it’s likely he will still get larger just not any more dramatically. He’s obviously squeezed most of his growth in his first year given the ideal conditions to do so but being only 1yr old should still slowly get larger over time mostly in thickness. I doubt he’s truly fully grown so young.
One thing I have noticed about many of the species in the genus Amtitlania (and their sister genera Cryptoheros) is that their size is often times limited by high nitrate concentration in tank water. (above 5ppm)
Aquarist sometimes suggest Cryptoheros cutteri is a small species, yet in my nitrate limited tanks they get large.
The male below easily hit over 8¨
Same for Amatitlania sajica, where the male easily grew to 8¨+
Females barely hit 5¨,but males almost double that size