Good call — the ad is indeed from 1966. It appeared in Boy’s Life magazine.
http://www.snopes.com/vintage-daisy-gun-ad/
1966 would have been my guess too based on the styles and the poses. That was sort of the last year of the mid-century apogee as things were on the edge of breaking loose in 1967.
I was 16 at the time and remember 1966 well. And you're right the very next year was the ushering in of the era we live in now.