Megan was wearing a bikini in the debut of Mad Men season 6 and it just looked off to me, it looks more like a cusper or 1970s and beyond to me. Dons trunks were fine, but Megan, not so much. Maybe it’s the way the ties on the sides make it look more skimpy. While the bikini did show more skin in the1960s, the waist lines weren’t all that low until very late in the decade. The leg lines are right so maybe it is closer to 1969.