healthy human brains are language sponges (my term) when a person is young but changes occur in the brain at about the time of puberty that change that dramatically.
I went to a school that offered a once-a-week Spanish class. I started in 3rd grade. While I can’t claim to be fluent in Spanish, the Spanish I learned then I know as well as English—I don’t have to think about it, I just know it. Languages I’ve learned since always require me to think about what I’m trying to say, how to conjugate verbs, etc.
Offering foreign languages could and should start in Kindergarten—maybe even a couple and continue through grade school/jr. high.
If you want to learn another language, one good way is to listen to music in a foreign language.
I did that with Polish and it’s helped me a lot.