What is the age and value of FN 16 gauge Belgium made browning serial number X56168?

No FN serial number data in the public domain.Ah but there is.With the serial number that you have provided,your Browning auto-5 shotgun was made by FN of Belguim for Browning in the year 1951.A Belguim made Browning auto-5 shotgun will bring between 350-550 dollars for a example displaying between 60%-80% of its original finish,and a good bore.