I do not grind anything at all for Scottie...I follow the Prey Model, which does not require any grinding. I posted an article about beginning the Prey Model diet a few pages back, so maybe you can take a look at it and see which model suits you better

Nope, it's not too young to start at all! In fact, when I had Scottie's pups with me, I also feed them raw as is (meaning with bone on) since they were 7 weeks old Easier bones like ribs or keels or backs help them adjust faster. When they're older you can give them harder bones like wings or drumsticks. Puppies take to raw easier than adults in my opinion...they adjust really quick and it's a joy to watch them eat and enjoy the food
However, I don't think it's necessary to feed bone ALL the time...you would need to monitor your pups to see if their poops are getting crumbly. Too crumbly or powdery indicates too much bone, and you could probably feed them boneless meats for the next one or two meals. For the prey model, bones are only 10% of the amount of food we're feeding, so it's really not much. Read up more on the Prey Model first before embarking on it, as you need to know EXACTLY what you are feeding to your pup