If the Chinese language is really such a notoriously difficult language to learn (and to speak) there ought to be no one using it anymore, right?
When we're young, we benefit from massive plasticity in our language learning skills, and of course any child who learns Mandarin (and sometimes Cantonese as well) is going to make a much better native speaker than I am ever going to make, despite the fact that I've devoted years to it and am highly motivated.
It's not just learning words. It is how things are said, references to metaphors and myths and such, and the fact that it is not a "spelled" language; the characters you're familiar with each represent a word part or a word that means one thing on its own, often something else in combination, and very few of them are used the way we use them in western speech. About 2000 of them constitute (approximately) high school literacy. But there are about 50 thousand of them. Bad enough? Oh no. A while back, Those In Power decided they were to o hard, so they "simplified" a bunch of them. Great, right? So you only have to learn the simplified ones, right? Wrong. The traditional ones are everywhere, and plus, some places in asia use the old ones, not the new ones. And then...
(Very) simple example. In English, I I ask you if you want soup, you might say "No." Easy, right? So you how to say no, (Bu Shi) Now you know what to say if I ask you about the soup and you don't want it, right? Wrong. In Mandarin, the question of if you want it is composed, literally, "want not want", (yao bu yao) to which you are expected to answer either "not want" or "want." (Bu yao) or (yao). And down the rabbit hole we go. :)
Trust me. As an adult English speaker, you go into learning Mandarin thinking it's easy, you're in for a serious encounter with your limitations.