Actually, definition a. does not refer to people, but to the accomplishment, deed or event itself.

So 'prodigy' cannot refer to an adult, even with the enhanced definition.

dictionary.com:

"1. a person, esp. a child or young person, having extraordinary talent or ability"

Cambridge Dictionary:

"someone with a very great ability which usually shows itself when that person is a young child"

So there doesn't seem to be consensus on whether only a "child/young person" can be a "prodigy", at least not according to the various dictionaries.

Is a 50 yo who first starts piano and is able to advance at the same rate as a child who is considered a prodigy not a prodigy? If not, is there another term for someone showing similar great ability but at an older age?

The dictionary I have sitting around (American Heritage)reads "A person, esp. a child, with exceptional talent" By this definition I would say the word can refer to an adult, but normally isn't used that way.

Oxford English Dictionary:
c.3.c A person endowed with some quality which excites wonder; esp. a child of precocious genius.

OK, I'll get pedantic here, I merely said that the enhanced definition in the preceding post did not allow for the interpretation that an adult could be called a prodigy. I literally meant what I said, and did not mean that adults could not be called prodigies is people wanted to call them prodigies. Honestly, called them pepperonis for all I care!

Pepperonis has no meaning, I prefer to call them anchovies myself (adult or fry).

Whew.. we got that. Now all we have to do is all agree on what 'extraordinary talent' or 'great ability' means.

Then we can all agree on what prodigy means! And we can all throw a big party and stand around being 'correct'!!

And we will develop a ranking system for musicians, so that we can differentiate prodigies from non prodigies... because.... that's what we want.

We're close guys I can feel it...