Hobby fish properly maintained, which very definitely does not include matching wild conditions, stay healthy and reach or exceed wild size (common among the rift lakes species) and live far longer than their wild counterparts.
As far as the OP: Most fish grow fastest when young, especial before puberty. Fish never stop growing, but do so very, very slowly when mature to old. So growth rate is inversely related to age. Growth rate is also controlled by the health of the fish and the size of its tank. So you are very likely correct in that you fish is smaller than it should be at a year, and that is possibly likely due to IPs -they no doubt slow it down. Is it thin at all?
But tank size also matters. You will only see very rapid (normal) growth in young fish if they are in a tank that in no way limits their activity and swimming space. The all-but-standard practice of moving fish from one to another, larger, one as they grow is unlikely to achieve maximum growth rate and full adult size. If the fish is housed initially in the tank in which it will live permanently, it will most likely meet the rates and maximum size seen in the wild. But it will also then live to a much greater age in captivity than the average wild fish achieves.
Your fish is still immature, so can essentially 'catch up' with the normal growth rate and size