Energetic fives?

Hi! everyone.

Could you tell me what "energetic five" means in the para below? Its excerpt from "Goodbye, Mr Chips" by James Hilton.

It was not that he was less active; he could still knock up a half century on the cricket field; nor was it that he had lost any interest or keenness in his work. Actually, too, his hair had been graying for years; yet now, for the first time, people seemed to notice it. He was fifty. Once, after some energetic fives, during which he had played as well as many a fellow half his age, he overheard a boy saying: "Not half bad for an old chap like him."

Thanks!