Hello, our Toby is fed partly raw partly kibble. Can't remember the exact age we started, but he's 20 months now and have been doing it for quite some time. He's doing really well on it too with usually nice firm poos. He gets minced raw for breakfast (in a kong) and kibble for tea (in a pyramid).
We did change his kibble at some point to a different brand. In the past, when we changed brands with our dogs, we used to do a very slow proces of mixing old and new. This is the most common method, I think? However, this time we did it differently; we fed him just his raw food (twice a day) for a few days and than started the new kibble full on. Had no problems. But perhaps others have different experiences?