At 2. Mine will be 2 in January. Friends ask what its like to have a toddler and I tell them its like having the pet monkey I always wanted as a kid.
At 2 this kid is just like a little chimp - cute, mischeivous, no words - just cute jabber and monkey noises, but she can climb anything and is fully capable of passing the monkey and bananas test. Pretty fun.
OTOH, you can't take a monkey to a restaurant like we could when she was a baby. She takes more effort to keep from trouble and the tantrums are a drag.