How do I know if this ad is vintage?

[drc]

I'm not familiar with these (though have seen them for sale), but if you have a decent microscope you can determine if the printing is consistent with the 1951 era. I've had people send me super close up photos of printing via email and I could tell. I know what type of printing was generally used for such an item at the time.

Another simple, though inconclusive, test would be a black light. A modern reprint would more likely fluoresce brightly. The test is inconclusive because they introduced the fluorescing paper chemicals before 1951, but much more likely that the 1951 paper wouldn't fluoresce brightly due to its old age and that they didn't as often use the chemicals in paper then.