A little over a year ago, my two best friends and I sat in a chinese restaurant in Paris (because we felt a need to eat it in every foreign country, escargot be damned), talking about our return trip to the city in 40 years.
The idea of re-living our backpacking trip forty years from now arose when we were in Barcelona and learned that La Sagrada Familia is believed to be completed somewhere in between 2020 and 2040 (2028 to be exact, but the Spanish don't seem to be overly optimistic that it will ever be really completed). In any case, given this excessive range of years and the assumption that we're going to get a little caught up in families, careers, and the craziness that is life over the next four decades, we decided at about 60 we would be ready to recreate the trip and see how Europe evolves in that time.