Old postbox

This lovely old postbox was on my walk today. I've seen it a few times before but never taken a photo of it till today. 

The royal cypher on it (G R) stands for George Rex (ie. King George) and I'd assumed it probably meant the box was from the time of the more recent George, who was Queen Elizabeth's father. But on looking it up I've found out that this particular cypher would have stood for George V, who was the Queen's Grandfather and reigned from 1910 to 1936. So in theory the postbox could be one hundred years old or more.