When? Gravity just means that you have to work hard to fly and it took quite a while before the amount of work you could do and the amound you needed to get in to the air matched.
I've heard similar things about people thinking the speed of sound couldn't be broken before Chuck Yeager. Rifle bullets could do it easily, but it took a while to get an engine powerful enough to get the speed and wings strong enough to not snap off the plane. But it was never a physical law.
Don’t get your panties in a bunch sonny I’m only kidding...