And they say Kamara was washed.

I don't disagree. I'm just saying he can't pull away from guys the way he could his first few years. Some of that is I think he put on 10 or so pounds of muscle to handle the grind of a season. So, it may not be age related.
I agree with this and it's relative to him player, not to other players. If he once had 6 speeds when he was younger he has 5 now and could lose another one at any time, as is the trend with running backs. He's still playing good today, but his abilities have diminished and will diminish further.