Connotations of using "boy" by upper-class liberal Britons in beginning of 20th century
Solution 1:
I apologize in advance for not being able to provide a more well-documented answer, or even a whole answer, but I did find this.
From: Eureka Encyclopedia
Boy (Broad boy; Buff boy; Business boy; Call boy; Career boy; Come-on boy; Fag boy; Party boy; Pratt boy) Male prostitute.
it also lists
Rent Boy
and
Baggage Boy
Solution 2:
Sample usage,
http://en.wikipedia.org/wiki/Mad_About_the_Boy
written by Noel Coward (smack in the middle of your demographic), clearly uses 'boy' to mean adult.