It's much healthier to feed the snake less often than 2 times a week (except with hatchlings). If you feed it too much too often, you can end up with a fat snake that won't live as long as if you grew it up slower.
Are you sure you really want to get a cornsnake? If you just want a big snake that is fairly calm, you might want to try black milksnakes. I don't have one yet, but from everyone I've talked to that does, they are very mellow snakes and they get to be an average of 6 feet long.
The only drawback is that only a few people are breeding them and therefore they are more expensive (between $75-200, depending on the breeder; most are listed at $150).
As far as corns...With my feeding schedule (twice a week up til about 6 months, then every 7 days til about 1.5 yrs, then every 14 days) mine have reached 2 feet at 7-8 months, and 3 feet at 20-22 months. I don't have a snake that is 4 feet.
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alstiver@hotmail.com
1.0 '01 Hypo snow cornsnake (Tesla)
0.1 '02 Ghost (pastel) cornsnake (Banshee)
1.1 '02 Bloodred cornsnakes (Desi and Luci Too)
0.0.1 Northern water snake (temporary pet)
0.0.4 '03 American toads (temporary pets)
0.0.3 Goldfish (Kabuki, Isamu, and Yuki)
1.0 American Eskimo mutt (Rusty)