When he’s a grown man who works in a stable, would seem to be the answer.
The Macmillan English Dictionary defines a lad as: ‘a boy or a young man’ or ‘a man who does things thought to be typical of young men, for example drinking a lot of alcohol…’
Put the word stable in front of the word lad, however, and you could be talking about a man of any age whose job is looking after horses, especially racehorses. When,during the Cheltenham festival a few weeks ago, Conor Murphy won £1m on an accumulator bet on horses from the stable where he works, reports of the event had two striking features.
One was the general pleasure in his good fortune; the other was the fact that everyone concerned referred to him as a lad, even though he is clearly well past the age of majority (his age was variously reported as ‘in his forties’, 30 and 31). The headlines were almost unanimous in referring to him as a stable lad while his employer, the racehorse trainer, said:
It’s absolutely wonderful, he’s such a lovely lad.
or perhaps
I’m thrilled. He’s a lovely lad.
or even
He’s such a lovely lad, one of the nicest you could ever meet.
depending on which report you read. The BBC’s Clare Balding, meanwhile, tweeted:
The lad who looks after Finian’s Rainbow had a 5-timer on Nicky Henderson winners & has won £1 million!
As well as not necessarily being either young or given to rowdy behaviour, it seems that a lad may also be a lass, since a search of the Oxford English Dictionary entry for lad reveals the following, with a citation from a Dick Francis novel to back it up:
1c. A stable-groom of any age; also, a female one.
I called on the trainer, whom I saw almost every time I went racing. ‘Did you find Sandy Willes?… She’s one of my best lads.’
There is a female equivalent of stable lad – stable girl – and a gender-neutral term stable hand, which some newspapers used in their headlines. However, incongruous as it may seem to outsiders to refer to an adult man as a lad, this appears to be the preferred term in racing circles.
Mr Murphy’s piece of luck had another effect: in the week of 12th-18th March, lookups of the term stable lad in the online Macmillan English Dictionary increased almost one hundred-fold compared to the previous week. Obviously I’m not the only person who was struck by this slightly odd use of lad.

Great post Liz. ‘Lad’ is also a common suffix for racehorses themselves. A quick trawl through Google has produced, Windsor Lad, Codden Lad, Bold Lad, Iver Bridge Lad – all winners in their day.