For the past two weeks I've caught Piper humping several times already and he's only 15 weeeks old. He has humped my Chi, his own brother, and my leg...have a pic of that one
Here is the thing...I was told by my vet that it is a show of dominance. My FEMALE Chi, Pixie, humps my Boxer on occassion while he is laying down. She'll attempt to climb up on his tail end while he's resting and go to town. It's not only a male thing AND it's not a neutering/spaying thing. Pixie is a female and was spayed at several months old. The vet said it's a dominance thing...Nothing like seeing a little girl Chi "huckle-bucking" a Boxer...that's what we call it.
I was told to wait until Piper is 6 months old because of the teeth thing too. Our vet does the laser also. I was also told by other people that the earlier you spay or neuter the smaller they'll stay...lack of hormones to bulk them up or something like that. Not sure how true this is or not but wouldn't risk my Piper's health to find out.