The day i brought Atticus home at 8 weeks, he was up and chasing a Kong soft squeaky toy and bringing it back to us to throw it again. That was within an hour of being home. As he grows up, he's definitely grown into a high prey drive almost 4 month old. if something is moving, he is after it no matter what it is. that probably started as a 12 week old. when the wind would blow and leaves would skitter across the driveway he was chasing them.
I'm sure it all depends on the puppy, but it started showing up very early for Atti.
Atticus - sable GSD 5/9/14
Luke - 4 y/o holsteiner/paint horse
Harvey - 1 year old female rescued tortoiseshell