I have an Arabic friend who's 17 and his older brother is 20-something. My friend still speaks with an accent yet his older brother speaks with a completely normal American accent.

Perhaps it is easier to pick up on accents and such when you're younger, but I don't believe it is easier to actually learn/master languages when you're young. Most people master languages when they are older, as far as I would know.

BTW, I have never heard anyone say "one three three seven." I was expecting a hax0r worthy definition of 1337 from you, Dogboy! Shame!