How Did People Get Into Train Spotting as a Hobby?

When did people start getting into train spotting as a hobby well there is a key moment I suspect there were train sponsors before the second world war. A guy called Ian Allen who was a railway clerk decided to print out a list of all the locomotives that there were and started a business out of this. It became immensely popular for young boys it was largely boys to get hold of the loco spotters annual and to stand up platform edges and take down the numbers of the various locomotive that went by.