The only reason I suggest Glutamine is that it helps muscle cells recover. I haven't "noticed" it's effect directly but I haven't gone cold turkey on it either.
I know the fatigue you are talking about. When I'm doing all the right things and I get it, there is usually something else contributing. Not saying that what's happening, but I would definitely examine stress sources. The human body is an amazing thing, but in terms of stress it has a hard time distinguishing the good kind from the bad kind. It tends to react by default to all stress being the bad kind. So exercise stress gets blended with all the other stress in our lives.
In terms of that downhill age thing...fergetaboutit
