physics - The Twins with a Different Age

Warning: To answer this riddle you need to have a thorough understanding of how time works.

Two twins were born during the same year, on the same month, and the same day, exactly 10 minutes apart. By the time twin A was 100, twin B was younger by more than 10 minutes, fairly slightly. Neither twin died during the 100 years.

How could Twin B be younger than Twin A by more than 10 minutes?

Answer

Due to time dilation, moving faster will make you age slightly slower. This is most commonly mentioned with astronauts and space calculations, but it can also be applied to lower speeds.

Technically, if Twin A normally drives his car at 50mph over the course of his lifetime because he wants to save fuel, whereas Twin B dashes around at 70mph because he's always running late, Twin A will have experienced more time than Twin B, so Twin B would be slightly more than 10 minutes younger after a century.

Thanks to Clint's comment below, there is a similar effect that could happen - gravitational time dilation. If Twin B lives in Washington DC (250ft above sea level) but Twin A moved to Denver (5000ft above sea level) at a young age, time will pass slightly more slowly in Washington because it's closer to the gravitational centre of the earth, again resulting in Twin B having experienced less time.