Being a kid in a culture goes a long way in forming how you speak. Your language is an expression of your culture. So much of my personality, how I speak, words I use, etc has been formed by what I watched and listened to growing up. By the time you're 20, it's past the time to form that same experience. The difference between this speaker and someone who has learned to speak perfect English in their 20's is that the former shapes the language as it continues to evolve while the latter simply learns (though that's not to say that late learners don't shape language.)
Being a kid in a culture goes a long way in forming how you speak. Your language is an expression of your culture. So much of my personality, how I speak, words I use, etc has been formed by what I watched and listened to growing up. By the time you're 20, it's past the time to form that same experience. The difference between this speaker and someone who has learned to speak perfect English in their 20's is that the former shapes the language as it continues to evolve while the latter simply learns (though that's not to say that late learners don't shape language.)