It all depends on the quality of the stock fish. The strain of which it has been born from etc.
Some strains of carp grow like the clappers. You can buy a 10lb carp that will be a 30 in 10 years. [usually imports] and you can also buy a 10lb carp that will probably never see 20.
However the amount of food going into a lake does have an effect as does the size of the lake. Each lake has a certain bio-mass, many match waters overstock the puddles they use and exceed the bio-mass with fish. Thus the reason why all the fish are mainly small and why they stay so small. High stock densitys can ruin small waters, especially if their isnt anything like mussels, crays, pea mussels, weed, pads etc for the carp to feed in or underneath. For example:
A water near me was created as a match water, and was stocked with far too many carp, amongst tench, bream, perch and roach. Somebody took it upon themselves to put a few pike in the water, and mussel beds spread when a nearby canal flooded. Now some of the fish are over the twenty mark. the lake record is 26lb and the lake is no bigger than 50 yards long and 30 yards across.
You look at waters with the largest carp in britian in...absolute fountains of natural food. Snails, caddis, mussels, crayfish, you name it and it's there and a sweep through the weed with your landing net will give u a good idea.
Bear in mind that most stock fish are stuffed with pellet based foods. So they do have the potential to grow large if that feed keeps coming. But most of the time it cannot. Thus the reason why carp born and bred in a lake are much sought after over your average stockie. Can't beat a good english original. Like the Leany Strain Carp. Bit of history and heritage in your hands. Pukka!
I've rambled on a bit there
Dunno if i've helped but i hope i have in some way.
Regards