Hi Unclepunk!
I'll assume by your name, and your height, that you ARE indeed a male!
There ARE a few proud yorkie daddies around here, but we could always use more!
So WELCOME, and I'm sorry that I can't answer your question knowledgably, but my UNeducated guess would be that yes, he probably still has a growth spurt or two coming up. I'm sort of in the same boat with a little girl that I'm hoping will continue to bulk up, but unfortunately, she's almost 10 months old.
Where'd you get your little guy?