According to kite's program...

[Doc]

How old is your Famicom? Mine's between 1983-1986, according to the program.

[kite200]

I gaurantee my program is accurate! haha, mine is between 1983 - 1986 as well

[kite200]

The research behind that was because the FF logo was added to famicoms after the disk system was released, and the round button replacement units came out after the square buttons were sent back in late 83, so therefore 1983-1986. I could go more in depth with the way the program works and such but unless someone really wants to know its not nessacary