How long until chivalry kicks in?

I was waiting at the bus stop when an elderly lady with a cane shuffled up and stood near me. The bench was occupied by 2 middle-aged women, another woman who looked to be in her 30s and a guy in his late 20s or early 30s. None of them moved.

I waited a good 10-15 seconds and then I turned to look at the guy. He was staring in the direction of the old lady then glanced up to see me giving him a look. He immediately asked the old lady if she wanted to sit down. She accepted and thanked him.

Perhaps he would have done the same without my non-verbal prompting, but what was he waiting for?