Cheryl - what does the D mean? No way to narrow down the age?
Not Cheryl, but the 'D' is simply a pattern mark. If a defect is found during QC inspection, they know which pattern to check.
From information posted on the members side, the identity of this item may lean more towards BSR Century series, even though the underside of the handle is not typical for a BSR. Lodge typically puts sizes at 12 o'clock, BSR at 6. The handle is the tricky part, until you find one of these with an original label still on it.
As far as age, 50's to 60's.