I need to know if your bottle has any numbers on the bottom right hand corner of the label? If not, then how about a date on the reverse side of the label? It looks like your bottle has a modern screw metal cap - and if this is correct, then Dewar's started using these in the late 1950s and early 1960s (replaced the spring metal cap). These are 'rough guidelines. Whisky.com does not provide valuations, therefore, contact one of these companies for this information - Bonhams.com or McTears.com Also, keep in mind they'll need very, very clear photos your any bottle you send to them. Make sure you get one of the closure and also one specifically of the label so that anywhere there's text, it can be read.