Mine is 5 weeks and I started her around 4 1/2 with just some warmed up soft canned food. she's still nursing full time but she's been taking a couple licks and tastes here and there. Once she's eating more of it I'll soften the puppy kibble with warm water and try her on that and offer her both.
Of course its hard keeping mom out of it. she wants to eat it all and poor baby gets none!!
So baby gets special feeding times by herself.