
Even the wildlings have a tradition of not naming their children until they're 2 years old. As you mention, it does seem that nearly everyone keeps track of their age & name-day. Having a lunar calendar makes it a lot easier for a common person with no training in astronomy to observe and measure the year. Luna orbiting Earth ~once per day is what causes a 12h tidal cycle. The seafaring sections of the book also make several mention of the tides, which would imply that the moon makes a fairly rapid orbit of ASOIAF's planet.

A year could be measured in terms of lunar cycles. Character's often speak of the "moon's blood" as a clear euphemism for menstruation, which is a reasonable clue that a lunar cycle is at least as close to a month as it is for Luna and Earth. The planet of "A Song of Ice and Fire" has a moon.


I have a theory for the second part of your question.
