This might be generally true, but is not always true. I, for one, have a condition where I cannot filter sounds. I cannot focus on any particular sound unless it is significantly louder than all surrounding sounds. No matter how hard I try, if you speak to me as a train goes by, I will not be able to understand what you are saying if my life depended on it. I have been through many tests and have been told it is an issue with the way my brain processes sound, not my ears themselves. As such I absolutely need subtitles to understand most movies.

As a side effect, I am easily able to differentiate even the most subtle differences in language. Although I am aware that most people cannot. It has given me an edge in language learning and have learned 3 languages as an adult. 2 of which I speak at near native level fluency and am constantly mistaken as a native speaker due to my near perfect accent. Still working on the 3rd. It takes practice and time, but I can imitate the exact pronunciation unlike many other language learners.

I'm sure there's plenty of other people like me out there who can also tell the subtle nuanced differences between similar sounds, even long into their adulthood.