Depends upon who you ask.
I'm planning on breeding mine when the females are 30 inches - either they will or won't. They may breed smaller.
Generally if you keep them warm and feeding first winter and brumate them second winter, they are at least 30 inches and very well may breed that spring.
Some will attempt smaller and have had success, some prefer 36 inches.
The cornsnake people seem to like 300g for corns but I don't know if there is scientific method involved in picking that number or if it just sounded good.
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11.14 L. getula californiae (Cal. King)
2.3 L. getula nigrita (MBK)
1.0 L. getula floridana (Brooksi)
1.1 Pantherophis guttatus guttatus (Corn)
0.1 Pituophis catenifer catenifer (Pacific gopher)
0.1 Heterodon nasicus nasicus (W Hognose)
4.2.14 Elgaria multicarinata multicarinata - (Cal. Alligator Lizard)