Agreed. My guess has always been it is because of lack of variety, not an intrinsic property of getting older. Take a summer off and travel to unknown lands, a

Agreed. My guess has always been it is because of lack of variety, not an intrinsic property of getting older. Take a summer off and travel to unknown lands, and when you get back tell me that didn't feel just as long or even longer than summer break did in grade school. Spend that same summer in the office or in your normal routine and it will fly by.