When I was 19 I started dating a 36-year-old woman. For the longest time we steadfastly maintained that our age difference wasn't an issue.
By the time I was 25 and she was 42, we finally started seeing that it was an issue, although we didn't call it that - we were simply at different places in our lives and we each saw different futures for ourselves. We also finally realized that we didn't treat each other like most couples did - we would go on separate vacations and such, talked to each other more like we were either roommates or blood relatives rather than people who were romantically involved - even though we lived together for more than 5 years. So after 6+ years together we split up, quite amicably, although after about a year we lost touch.
By the time I was 25 and she was 42, we finally started seeing that it was an issue, although we didn't call it that - we were simply at different places in our lives and we each saw different futures for ourselves. We also finally realized that we didn't treat each other like most couples did - we would go on separate vacations and such, talked to each other more like we were either roommates or blood relatives rather than people who were romantically involved - even though we lived together for more than 5 years. So after 6+ years together we split up, quite amicably, although after about a year we lost touch.