"I know I can still play, but it's like I told my wife, I'm just tired mentally. I'm just tired,"
I don't think I've ever heard a QB say that while retiring. John Elway's speech comes to mind right away. He said the reason he retired was because he couldn't do it physically. He even said he could do mentally but his body wasn't going to make it through another year. I can't say for sure about Montana, or Young, or Marino, or any of the other greats but I highly doubt any cited being "mentally" tired as the reason for their retirement. It always seems that the physical challenge is too great.
I called Favre coming back from day one...