Well, I would have to say yes and no. Regular handling helps to keep them dog tame, that much is true.
But adult corns I've bought from big breeders (Rich Z & Kathy Love) aren't extremely aggressive. If anything, they're more flighty and try every minute you have them out trying to get loose from your grasp. The two adult males I acquired are so much better than when I first got them.
Generally they don't get handled as much as those of us with pet snakes, or small enough breeders that take the time to handle their snakes consistently, not just for feedings and cage cleanings.
I guess that's just another thing about corns that makes them so great. Even wild-caught ones can be quite docile and less apt to bite. But then again, there are certain individual snakes that are aggressive no matter how much they were handled as hatchlings. I nicknamed my Phantom "SOS", Spawn of Satan, as he hated me with a passion. No matter how much I handled him and he bit me. I don't know what I ever did, but he'd defecate on me, musk me, tail whip me, bite and bite. I gave him to a friend, and he's been nothing but sweet to her. I guess its that whole 'birds of a feather' thing.
And some snakes are known for their attitudes. Kathy Love's Okeetee's generally have quite the reputation, my own Love Okeetee sure fits it. Sunkisseds are another one that people say can be hellions. So far the two 2005's I picked up this year seem to be little angels compared to some I hatched out myself.
But
most corns will get used to being handled, no matter their age when you acquire them or how infrequently they were handled as a youngster. Generally I don't even think about it when I'm buying a new snake.