the facts of life

Kazuo Ishiguroの "The Remains of the Day" を読んでいます。
DAY TWO - MORNINGから引用します。
‘I’m sorry to bring up a thing like this, Stevens. I know you must be awfully busy yourself. But I can’t see how on earth to make it go away.’
I waited a moment while Lord Darlington returned his attention to Who’s Who. Then he said, without looking up: ‘You are familiar, I take it, with the facts of life.’
‘Sir?’
The facts of life, Stevens. Birds, bees. You are familiar, aren’t you?’
‘I’m afraid I don’t quite follow you, sir.’
‘Let me put my cards on the table, Stevens. Sir David is a very old friend. And he’s been invaluable in organizing the present conference. Without him, I dare say, we’d not have secured M. Dupont’s agreement to come.’
‘Indeed, sir.’
‘However, Stevens, Sir David has his funny side. You may have noticed it yourself. He’s brought his son, Reginald, with him. To act as secretary. The point is, he’s engaged to be married. Young Reginald, I mean.’
‘Yes, sir.’
‘Sir David has been attempting to tell his son the facts of life for the last five years. The young man is now twenty-three.’
‘Indeed, sir.’
‘I’ll get to the point, Stevens. I happen to be the young man’s godfather. Accordingly, Sir David has requested that I convey to young Reginald the facts of life.’

"the facts of life" はその後に "Birds, bees" とあるので見当は付きますが、話す相手は２３歳にもなっている青年ですよ!? "the facts of life" の辞書の説明を見ます。

・Oxford English Dictionary: Information about sexual functions and practices, especially as given to children.: They were left to play in blissful ignorance until such a time, as they were old enough to understand the sexual facts of life.
・Collins Dictionary: n British English; the details of sexual behaviour and reproduction, esp as told to children:
・Merriam-Webstery: the facts about sex that are told to children: He explained the facts of life to his son.
・Wiktionary: (euphemistic) knowledge of sexual reproduction (almost always used with the)

それにしても、２３歳の青年が近く結婚するので "the facts of life" を話さなくてはと心配するのは、笑っちゃうね。