Counting age in Japan

Hello, i'm 17 and i'm going to Japan in a few months. Just wondering how Japan counts its age.
Does it count by years or years and months. For example, if i'm born in 1997 November am I 18 in January 2015 or still 17?
Thanks in advance

One is either 17 or 18. There's no "half" past your elementary school years and no one really mentions when they're going to turn the next age.

I think I understand what you're saying. In the past Japan had a system where everyone would change age with the new year, but that was way long ago. However, these days you would update your age on your birthday, so you would be considered 18.

You'd still be 17 until November 2015.

17, and being 18 makes little difference in Japan as 20 is the point were your considered an adult.

The old days there is how to count that kazoedoshi(数え年）, it was already one year old at birth stages.
http://en.wikipedia.org/wiki/East_Asian_age_reckoning
However, now it is one year old you come is the first year of birthday.
So, you're 17 years old.

However, these days you would update your age on your birthday, so you would be considered 18.

Whoops, my bad. I meant you would currently be 17.