There is a theory that the older a carp gets, the more refined/sensitive it's gustatory and olfactory senses become, so a "fresh" baited area, which is attractive to younger fish, is a bit much for the more developed senses of an older fish. Possibly uncomfortable, or just unnatural and spelling danger...Can't remember the guys name, but heard this on one of the carp casts a while back...…… This also adds to the theory of "big fish" baits, with less flavours and more focused on the right levels of nutrition.
Also, younger fish will have to eat certain foods/vits/mins to support growth rates. Where as a larger "topped out" fish can obtain enough vits and mins to "sustain" current size, via osmosis in a decent environment...… So, imo, there will be slightly different dietry needs..... I am talking very young fish, where experiments have been done with vit c, for instance, which is widely regarded as non essential in quantity for mature fish, however small fish will take in orally , as mentioned, to support growth rates.... Lets remember that not all smaller fish are young fish. But young fish tend to be small. I'll try and dig out the Carp Cast, there's a good 20 minute chat/interview.