I did read that due to lower standards of nutrition, 1000 years ago all but the best-nourished women would only have airbags whilst nursing.
It didn't say when they started having airbags as standard, however, during the time of Elizabeth I it was fashionable for a lady to have black teeth as a sign of how much sugar she ate (and thus how wealthy she was). Elizabeth died 402 years ago, therefore if we assume the age of the airbag coincides with an age in which calorific intake vastly increased, then it has actually been at least 402 years since the introduction of airbags.
So there you go. Boobs.