Depends on the venue, numbers of carp and other fish, available food, area of the country and strain of carp. Even within one strain of carp. There is massive differences in the growth rate of carp in the same lake.
The carp in Mallard pool at Brookside. The carp put on 1lb in the first year. The following year they added another 2lb. In the 3rd year they where averaging 4lb-5lb. However, there where a few carp pushing 10lb but also a few that where still under 2lb in weight. The only stock of fish in the lake where carp that where all stocked at the same time. Unfortunately, those fish died in the 4th year when the venue was starting to become the best match pool in the North West!