Would you consider there is an age limit to learn languages?
Are you including the ability to speak without a foreign accent? There are certain sounds in each language, that beyond some earlier age (12 or so perhaps?) one just makes a complete mess of certain sounds.
For example, since in my time many students took their first class in Spanish at age 14, they could not learn to "trill" (rolling the tongue along the palate) the "R" in words. The word always came out sounding like an English word for many students.
Also, the inability to make certain sounds correctly acts as a shibboleth. For example, the Jewish holiday in December, Chanukah is often spelled today as Hanukah (or Hannukah), since so many Gentiles cannot make the guttural "Ch" sound that some think is the sound of spitting up phlegm. It is a common word sound in Hebrew, Arabic, and German (hmm, hmm, hmm, hmm - don't that beat all).