Zimmer graduated from LJHS in 2009 where he played and was a member of the Cum Laude Society. He played first base, third base, and pitched 22.1 innings during his senior year. Zimmer batted .410 with a .492 on base percentage and a .701 slugging percentage, and hit four home runs with 23 RBI. On the mound, Zimmer had a record of 3-3 with a 4.39 ERA. He was named team MVP in 2009, and was also named to the San Diego All-Academic team with a 4.20 ERA.
He pitched a little at La Jolla (Calif.) High School but went to USF to play third base. With an All-America at that position, the Dons converted Zimmer into a pitcher and struck gold. In 2012 his stats were 8 GS, 54.3 IP, 2.15 ERA, 2.97 FIP, 9.94 K/9, 1.16 BB/9, 0.88 WHIP, and .218 BAA