For US instruments, the serial number will start with a letter. That letter indicates the decade. The second character will usually be a number. That number indicates the specific year.

What is the oldest guitar in the world?

Belchior Diaz Vihuela This particular vihuela – the predecessor of modern guitars – created by Belchior Diaz is widely considered the oldest guitar in the world. It dates back to around 1590, has 10 strings, and instead of regular metal frets, its ligatures are tied like those found on a lute.