Twenty can't be expected to tolerate sixty in all things, and sixty gets bored stiff with twenty's eternal love affairs.
Actors must practice restraint, else think what might happen in a love scene.
I remember many a time, going into someplace like Wrigley Field - where you could cut the humidity with a knife - and playing a doubleheader. I loved to play the game. It didn't matter if it was a doubleheader, or a single game, or a day game after a night game. I wanted to play.