Can Terrible 2's start at 1_1/2?

This is the scene of a wild child at the bank, running a muck b4 heading off 2 get his blood drawn. He ran in and out of cubicles and gave me quite a work out. I thought "Terrible 2's" start @ 2. Is it possible they can start @ 18months? He is a very sweet boy but, the energy, the curiosity is outrageous. At 3feet, he is so tall and strong, he can get into places that most kids his age can't. He can reach, turn on and off the light switches. He can get on top of the chairs in the eat in kitchen and use them to get on top of the table. He has even tried to use the chair as a stepping stool to get on top of the kitchen island. A couple of weeks ago, he jumped out of his crib but, I'll blog about that later.