I expect Charles will surprise everyone and take over the starting back position. People are really over estimating the problem with his knees. Coming back from an ACL tear is not like it used to be. All of the doctors I have listened to on the radio who know of Charles situation and have evaluated it say that it really isn't likely to be repeated. Once he heals this off season with recovery training he should be good to go next year. 

Charles is only 30 years old which isn't physically too old, even for a RB.  The reason people think Charles is done is because he had his injuries one after the other which kept him out most of the last two seasons. But it is not uncommon for one ACL to fail and then the other to follow in a few years.  However, once both ACL's have been surgically repaired, he should be fine.

I think people will be shocked at just how much better a back Charles is than CJ. Charles and Henderson will make CJ look like he is stuck in molasses.