Horny little devils, these Yorkies! My Higgins did it right from the gitgo at 7 weeks. And he still does! He is now 8 months old and was fixed at 5 1/2 months. HOWEVER, he only does it to his really soft baby blanket.
 
We have named the blanket "Susie" and we give it to him once in awhile. When Higgins is in the midst of a really passionate humping session, Don DOES remind him that he WILL get pimples and may go blind.......