It’s a bit of a forgotten area in railway history but as far as I can see bankhall provided steam locos for the services from Liverpool exchange to the north of England and Glasgow, and engines for shunting duties at exchange.
There would be some motormen signing on there to work the electrics but the electrics were maintained exclusively at Southport
His age is a clue to when he started, he would have to be sixteen.
The normal route to a driver on the railways was the same everywhere, join as an engine cleaner, maybe two, three or more years as a cleaner then start “training” as a fireman, a lengthy process maybe four or five years till you become a full time fireman, then wait your turn in the queue for becoming a driver.
That is the norm, but obviously varies a lot from depot to depot, and ww1 may have speeded up the process as it put huge demands on the railway.
Many drivers jumped at the chance to train on the electrics as it was less mucky and regular hours but very stressful as you have no mate with you, and it’s boring just shuttling up and down all day.
About 1904 sound right but it may not be possible to put an exact date to it.
He would be in a union, try the union records at Warwick university, I am not familiar with them, but others on here have mentioned them.
Mike