Green’s Dictionary of Slang

(US) inexperienced.

1891		(con. c.1880) Bourke On the Border with Crooke 204: There were sarcastic references to the lack of ‘horse sense’ shown by certain unnamed ‘shave-tail leftenants.’.
1959		C. Himes Crazy Kill 34: I’ve known you since you were a little shavetail kid on 116th Street.
1990		S. Morgan Homeboy 142: Up shot the shavetail Assistant D.A.
1993		T. Jones Pugilist at Rest 64: I remember that day far more clearly than the day Kennedy was shot, when I was a shavetail private just out of boot camp.