How is the twin that is born first younger? If you were to expand the time gap between their birth by a year, is the first child born still younger? I would personally say no.
Example: If the first child is born in 2008 and the second child is born in 2009...how can the child that was born first be younger then the child that is born second. The first child is 2 years old and the second child is a 1 year old. Therefore making the first child the older child.