YES, my Suzi was 8 months old and was always had them down, or one ear up and one down. I took her to a professional groomer, and they trimmed them and tapered her ears, like A Yorkie is suppose to look like, no problems now with ther ears.
Your Yorkie's ears could be just too heavy for him to stand up if their is A lot of hair.
Also it is very important to have the hair plucked out inside of the ears. Because the hair on yorkie grows all the way down the ear. A groomer does this too.
