Typically for females 3 years, 3 feet long, 300 grams - males whenever they are ready - often at 2 years, no matter their size.
While corns breed readily in captivity, so they will reproduce for you, but the bigger issues are around whether you are prepared to be a breeder - mostly are you prepared to deal with 15-30 hatchlings, get them started and find new homes for all of them, or deal with them til you can. While established breeders have markets and are able to sell or place babies, they can be a considerable responsibility to house, feed and care for if they don't all sell. Many times pet stores and friends seem like a quick way to place them but those don't always work out - so just a warning to be prepared!
mary v.