It's always been a rule in our dojo that you go at the pace of your uke. We have a man who is 61 years old and is ranked 2nd kyu but I'm not going to throw him as hard as I do the younger guys.
We have a kids program where they test up to 6th kyu and once they reach 6th kyu they stay in the kids program and get ready to test for 5th. Once they pass their 5th kyu they are allowed to train with the adults. Some of the kids (they're teens actually) have been training longer than me, and have really strong basics. But I wouldn't throw them as hard as the dans or other adults but not as soft as the newbie adults who aren't 5th kyu yet. One of their requirements to train with the adults is that they have to be able to take breakfalls. This seems to work really well and I look forward to training with them once they pass their first adult test.
In regards to you 2nd dan instructor, I don't think it's fair to expect him to be as good as an 8th dan shihan. We have several 2nd dans and they fill in at times when my sensei is away teaching his own seminars. I would never dream of challenging them or expecting them to teach like our head instructor who's a 6th dan.