Actually, studies have shown pretty much the opposite to be true. Within the first few years of life, most people have heard just about every sound in their native language, and within the next few, they will learn to properly reproduce these sounds. The ability to pronounce vowels and consonants specific to another language becomes much, much harder for most people as time goes on. That's why people can live in, say, the United States for 30 years, speaking primarily English the whole time, and still have a distinct accent. Without specific coaching/training, they will never quite get the pronunciation the same as a native speaker, because their mouth was "trained" at an early age to produce different sounds.
