In period fiction, I have seen a few times a father or other older male taking someone to a prostitute to lose their virginity. Common enough that it can't come from nowhere. Sometimes they watch. It is almost always shown as traumatic.
He was in the war though. The majority of guys who fought probably lost their virginity during the war to a prostitute. You're facing death every day, you might as well.
I looked at Wikipedia about Fleming’s schools and Eton and Sandhurst werelisted there… archetypical venues for that ingrained behaviour.
Fleming in that section of the article was highlighting that he personally had some axes to grind but kept them firmly out of his novels.
I don’t think paying for sex quite has the sting