There have been quite a few stories on that theme, but given the early twentieth century English setting, you may be thinking of "The New Accelerator", a 1901 short story by H. G. Wells, available at Project Gutenberg.
Plot summary from Wikipedia:
"The New Accelerator" is a 1901 science fiction short story by H. G. Wells. The story addresses an elixir, invented by a Prof. Gibberne, that accelerates all of an individual's physiological and cognitive processes by some orders of magnitude, such that although the individual perceives no change in themselves, the external world appears almost frozen into immobility and only the motion of most rapidly moving objects - such as the tip of a cracked whip - can be perceived.
Hmm. You're sure the main character is a boy? Must be some other story then.