Pablo's Mommy

Hi there. New to this site. I would like to ask for some opinions as to my Yorkie (I think), Pablo. One day after picking up my daughter from school, we drove up to see him sitting at our door step. He was so filthy & completely covered in fleas (but with a brand new black collar, go figure). After giving him a bath, which was a complete nightmare due to the thousands of fleas & blood red water, & giving him a haircut (it was so tangled) we fed him & immediately contacted The Lost Pet Hotline. No one was looking for him. We posted fliers & drove around our neighborhood asking if anyone recognized him. Nothing. So after a month of caring for him we decided he would stay with us. He is a very sweet, loving dog. Can someone tell me by looking at the pics I've posted if he's a full blood Yorkie & about how old he is? I know it's a long shot but I'm hoping someone here can give us a clue. Also, any Yorkie tips would be very much appreciated. Thanks you guys