> It seems like it's far easier with early exposure to languages. I speak six languages, and don't find languages too difficult, which I attribute largely to having grown up speaking two languages from two different language families, and being exposed to a third one fairly early.

I think it's more along the lines of: Your first/native language isn't a problem, your second language is difficult, and with each beyond that it becomes easier to change how you think to fit the next language. It's just, being exposed young breaks that second-language hurdle early enough you don't really remember it being extra difficult.

I'm not fluent in anything besides English (though know a small bit of Spanish and Japanese), so take that above with a grain of salt. But the difficulty curve seems similar to programing languages, where the more you learn, the more you recognize underlying concepts across languages, making further ones easier to understand.