When did the number of holes on a golf course become standardised at 18?

Question

A course with 18 holes became the standard number in the early 1900s. St Andrews led that trend, changing its course from 22 holes to 18 in around 1764, and gradually other clubs began to follow suit. Before then, courses with any number of holes, from 12 - 25, could be enjoyed - or perhaps endured, depending on the player...