Neuroplasticity does drop with age, but the drop is smaller than it was previously assumed to be, especially outside of early childhood (you may note that eg. this graph starts at 20 years old)

this is like saying you can't run after 30, yeah sure it generally becomes less trivial but if you actually try to do it and don't do it in the worst way possible it's absolutely doable without much struggle.

kids absorb language like a sponge, adults are like silica gel, just expose yourself to the target language often and you'll learn it. The problem is that many people are horrendously impatient and try to brute force language learning in like 2 months by memorizing individual sentences and shit, which isn't how our brains work..

It helps a lot that they're completely immersed in the language, by people who want to help them learn, and they desperately need to tell us things with no alternative.

Children absorb language like a spknge because they are forced to by necessity. Moved to a Spanish speaking country and in three years I could run linguistic circles around any three year old. (half joke but you get the point hopefully)