Yamaha offers a convenient serial number wizard on its website to determine the age of instruments.
If you are having trouble determining the decade in which your Yamaha guitar was made, try taking the instrument to a guitar shop and ask if someone can help date the guitar.
Nylon-stringed guitars have always been poor cousins to the steel-stringed instruments favored by contemporary musicians, but classical and Flamenco guitars produce some of the most beautiful sounds to emanate from an acoustic instrument.
Historically, Spain has been a center for classical guitar makers, as has Italy.
Yamaha's guitars serial numbers repeat every 10 years, so additional research may be needed to find the exact year your guitar was made.