Out here in the East of England my father is 'old boy' at 85, so is my great nephew who is 5!
All males are called or referred to as old boy, as all females are referred to as old girl, irrespective of age.
We know our own colloquialisms but are not too keen on some others…
An old boy was standing outside his house in a rural village in Suffolk when a big shiny 4×4 pulled up beside him, driven by Londoners who had just moved up but who didn't know their way round yet.
"Hello John, can you tell me how to get to St Margarets?"
"How do you know my name is John?" said the old boy.
"Err…well, I guessed" came the reply.
"Best you guess your way to St Margarets then!"

Andy