If you look in this forum (General Yorkie Discussion) there's a 'sticky' with a puppy growth chart. You can look up his current weight relative to his age and see how much you can expect him to weigh full grown.
Where is this lady coming from to meet you half way? I'm actually looking for a yorkie on the "bigger" side (they're all so tiny to me!) between 8 - 12 pounds. If you get any good leads, let me know