I feel the same as many of you, but I don't think age has much to do with it. Like Mike Gundy, I'm a man, I'm 40, and I still get pumped for games. I've got an isolated gym/mancave where I can put on a game and get as excited and stupid as I want. I can, and do, still yell at the TV and jump around like an idiot.
But not for Cowboys games. Like many have posted, I'm sort of numb now. I think it was all those historic blown leads last year and the incredible late game bungling we all saw. This team is extremely stale right now and needs a real makeover.
And I guarantee you we aren't alone. For years I've watched most games at a Dallas-area bar/restaurant with some friends, and you can feel the apathy growing the last couple of years. From 2006-2009 or so, people would come in with their jerseys on, get really into the game, etc. Now there's just a scattering of people who even pay attention, and even they are pretty subdued.
The really bad thing I've noticed, and this just started happened last year, is that when watching a non-Cowboys game in which I have some kind of rooting interest, I now expect the worst. If a team I like is winning, I expect them to blow it. If a team I hate is losing, I expect them to come back and win. I'm naturally pretty optimistic, so when I caught myself feeling this way late last year while watching a game, it surprised me. I realized that my Cowboys feelings had bled over into games they had nothing to do with.