Value of 40 year old mens rolex perpetual?

There is really no way to determine the value of a Rolex without seeing it, opening the case, reviewing the serial number (either numerical, Roman Numeral plus two digit year, or a letter preceeding a number). Also, what type of Rolex model is the watch? I will tell you that when I was in a jewelry store in London the owner admired my 1950's vintage Rolex and offered to swap me for any Rolex in his display case (except the President model). Most of the President models retail for around $16,000 up to about $32K.