Twin Paradox??

[BMAD]

Anna, the older twin, was born three hours before her younger sister Lana. On Lana's 21st birthday, they both went out to a club with some friends. The bouncer was checking ID's and let Lana go in. But when the older Anna tried to follow her in, the bouncer said, "I'm sorry, your 21st birthday isn't for another two days." How is this possible?

[bonanova]

Between their births, two things happened:

1. The clock struck midnight
2. Their ship crossed the International Date Line.

[ParaLogic]

Anna was born the evening of February 28, on a non-leap year (say 1991) at around 23:00. Lana was born three hours later at 2:00 on March 1, 1991. Twenty-one years later, it is 2012, a leap year. On February 28, Anna turns 21. But Lana doesn't turn 21 until after the extra day of February 29.

Edited April 16, 2013 by ParaLogic