curmudgeon - ‘An avaricious churlish fellow; a miser, a niggard’ [Johnson]

I'm surprised at the good Doctor's definition. I had never thought of the term applying in any but the final sense - perhaps usage has changed or refined over the centuries. And I have certainly been acquainted with young curmudgeons (although, admittedly, not so many as old ones, who seem to abound!)

The use of "old", in the UK used to have little to do with actual age - it was a sort of term of endearment, as in, "What are you having, old chap?" When I first moved in to the East Midlands I was amazed to hear men talking about their "old boy" in terms which did not befit the grandfather to whom I thought they referred. In fact, they were referring to their young sons.