Looking up dictionaries I don't see a easy rule when to use ability vs. faculty in sense of a describing attribute . For example, "cognitive faculty" or "faculty of speech" seem to be standard terms, but then "learning or mental ability" seems more common than "learning faculty". The only pattern I see is that abilities are kind of innate(?).
To me, and I don't think there's a Chicago or AP reference on this so YMMV:
So, an infant has no faculty of speech, and a toddler has faculty but limited ability.