A.J.
This is not early. My older two attempted fits at 18 months, but my youngest started at 6 months!!!! No matter, you can stop them with discipline fairly easily since they're new, or live with them for the next several years (as they get worse if you ignore them).
My oldest learned quickly not to throw them at home at 18 months, but around 2 1/2 she started throwing them in public ONLY. (she's no dummy) Finally I had to discipline her once in public so she knew the rules would be enforced there too and she stopped. Let me know if you want the discipline approach. It has saved my sanity home alone with 3 under 5 while husband travels constantly.