[Mew]

You know, I could have sworn we'd talked about it at some point, probably in relation to the "Big Picture" episode - but I just checked back through the threads for it and couldn't find anything! Most of the discussion was about the photos themselves (Frankie appearing in about 30 of them even though she's not meant to be that old, if her presence in them meant she LIVED at Foster's all that time, that sort of thing) and not specifically the chronology.

I do remember a decent amount of discussion about how old Wilt was/what year-decade he was created in, though.

I imagine there's no "official" answer since they probably wanted to avoid 'dating' the show with specific years and/or figured it wasn't that important to bring up. Late 60s/early 70s sounds about right to me, though.