I've given this some thought as I am in the same spot you are. Although you may say age has something to do with it, I feel the biggest factor is experience. The more exposure and experience you have, the less the desire to play. When you are first getting into gaming, everything is new to you. All of the genres, the different approaches to games... you find worlds and things you can build. The investment is rewarding. However, as time goes by and as you play more and more, the noticeable variations become less and less. There maybe some new mechanics, however you will never obtain the same feeling unless it goes beyond the skin, theme, slight mechanic change, variation stage.
For example, if you played a lot of Masters of Orion 2, that game was ground breaking at the time. All that has sense followed has been more and more variation of the same and now you are playing MoO 5.0. I think it feels the same and thus your attention is like, have been here and done this and interest is held less. EU IV is a great game, however it is on iteration 4 now, I mean if you started from the beginning, you have played the same game a lot! Never-mind the changes, the core theme is still there.
So I feel yes age, but coupled with that is experience of playing...... it is the been there done that syndrome. Compound all this with work-life balance and that makes things a lot tougher and adds a whole new equation...... as there now has to be a lot of value in the game as time is more limited. There is a lot that goes into the weight of play here.....
