As an avid language learner myself, I would be inclined to agree, were it not for the fact that about half of my father's siblings really have no aptitude _at all_ for languages.

One uncle has been living in France for over 40 years, but anyone can still hear he’s a foreigner, most Dutch will immediately recognize his accent as Dutch, and many can immediately pinpoint the region he grew up in. (Part of the reason is probably: he himself doesn’t care. He just talks —sometimes with hands and feet— and his interlocutors manage to pick up enough of what he says to suit him.)

An aunt used to live in Brazil for years, and never could get the hang of Brazilian Portuguese. Her son has been living in Brazil for some 15 year now, and is still not fluent in the language...

People's ability to pick up languages can be totally unrelated to their general intelligence.

That said, I _personally_ agree that immersion is the best way of learning a new language. But it still does take time, and you've got to have the opportunity.