Nikko, 4 months old and we've had him for one month, is pretty good at sit, and sit and stay (for up to about 5 seconds). 4/5 times, probably, but always needing the treat as part of the equation.
The only trick he's totally reliable at is "high five" which is him going up on his hind legs and tapping both his front paws on our hand which is up in a high five position.
Not much yet, I know, but we're still working. :-) I look forward to hearing what's in other yorkies' bags of tricks! And even more at how old they were when they learned them - great question mina0710!
Thanks!
Lauren & Nikko