cut teeth
cut teeth {v. phr.}
1. To have teeth grow out through the gums.
The baby was cross because he was cutting teeth.
2. or cut eye teeth {informal}
To learn something very early in life; gain experience; start by learning or doing. — Used with a possessive, usually used with "on".
The professional ball player cut his teeth on a baseball bat in the sandlots.
Mr. Jones's company is building the new Post Office in town but Mr. Jones cut his eye teeth as a carpenter.
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Source: A Dictionary of American Idioms