As a child, 3 months - an entire summer in Europe in the late 1970s. I have a few memories and lots of photos.
During university - 5 weeks backpacking Europe with college buddies and an Interrail pass.
Since college - 4 week honeymoon (Hawaii, NYC, Paris) and a 3 week 10th anniversary trip (India, Nepal)
When the youngest kid gets dropped off at college, a 4-6 week trip will be high on our priority list.