Alex,
Neither of you is “right” and neither of you is “wrong”.
The primary “rule of thumb” in the practice is to find, determine or “discern” what is appropriate for you. This determining is completely free of the determining going on right next to you with your friend.
By this I mean what is appropriate for you only has to do with your life, your path, your svadharma (life mission). In the yoga context the soul has come into the physical body to fulfill a purpose (or purposes). No two are alike. Some are here to rest in the gutter while others are here to run a large software company. The key is to be able to find your own unique purpose for being AND not be deceived by your ego along the way.
Speaking more to the point of your post, I have found some teachers that are “new” and “young” to not have any idea what it is like living in an older carcass. I’m in my late 40s and can completely understand what a young body feels like, having had one a short while ago. However I would not presume a new teacher was a poor teacher due to this. It just requires a bit more on their part to be “good”.
Older teachers DO know the body but can become rigid in their thinking, stuck in their teaching, and loose sight of the larger picture thus burning out. But I would not presume an older teacher had this perspective, it would just require a bit more on their part to be “good”.
The resolution to your discussion is this:
Your friend is well served by a teacher with ten years of teaching. Fine. Good for him. He should seek a teacher that serves him, as his needs change, so too should the teacher.
You are well served by a sound teacher with no regard for their tenure. You should find a sound teacher and continue to learn from that teacher as YOUR needs change - so too should the teacher.