I took three years of Spanish and got an A every semester. Even when it was still fresh in my mind, I was nowhere near able to hold even a very simple conversation. And now just a few years later it's all totally gone from my brain.
My mother's native language is Spanish and she never taught me, which I resent her for. But I still find it incredible how shitty my public school education in Spanish was. We really should be teaching kids a second language from kindergarten up.
No offense, but I despise this kind of essentialist thinking, that once you're past a certain age it's all over. It's the way languages are taught. Comprehensible Input is where it's at. Take a look at the first five min of video link nested below (the bot removed the comment b/c it had a youtube link). You can watch the rest of the vid but the main part is from the first five min.
well it's certainly not "all over" if you don't learn a language young, but it's going to be more difficult to become bilingual from a developmental perspective (less neuroplasticity) and a practical perspective (typically less time to spend learning due to adult obligations)
Language acquisition research on a "critical period" for language learning is inconclusive. Neuroplasticity may make it easier for a child to acquire/differentiate specific linguistic information (e.g. sounds that exist in one but not both of the languages) but being socialized into a second language discourse community /also/ means that they're getting far more time practicing the language.