I learned Spanish in my 30s, but was immersed by living in a Spanish speaking country. Though, I've spent a lot of that time alone, so my level is not where it could/should be. But I can talk confidently with anyone about almost anything.
But I really don't think there's any mental hurdle to learning a language at any age. In fact, I think it is EASIER to learn a language as an adult (as opposed to child) because you understand language in general, and so many other concepts.
There are two reasons that adults have trouble learning a language:
1. time. Adults have endless responsibilities, which make it difficult to dedicate the time required to learn.
2. Lack of humility. Not being able to communicate in even the most basic of terms can be humiliating, if you lack humility - as most adults do. You need to be able to completely put aside your pride, and just be eager to make mistakes endlessly.
There's a lot of language schools here - both to learn Spanish and English - and I've met so many people who are "trying" to learn a language and refuse to practice out of fear of making a mistake. At no point have I ever felt even the slightest bit self-conscious about my Spanish, and I simply just try to communicate as fluidly as I am able, even while knowing I am making mistakes. When I learn I've been making some mistake for sometimes years, I simply laugh.
Similarly, there's plenty of locals (and people around the world) who have learned English to a reasonably high degree. So it is clearly possible. Though, even amongst them it often find that there's a genuine hesitancy to talk to me, a native English speaker. Their motivation was simply for a higher paying job, and evidently they swallow their pride for $ and pain.
I can recommend https://languagetransfer.org as an excellent resource, if your target language is covered.
And also just to focus on the basics. I recommend people don't even worry about verb conjugation when starting. Just speak in infinitive exclusively.
I eat bread. Tomorrow/yesterday he eat bread.
People will understand 99% of the time. Just focus on getting vocabulary, confidence and fluidity. Add verb tenses in due course. Again, it takes humility to speak in completely broken sentences, like a little child. But that's the only way.
the conjugation thing is really interesting and you're right you should just plow through with mistakes, even knowingly.
One thing you notice in kids in their native language is they get the trickier/irregular parts of grammar wrong all the time and repeatedly, as in they are corrected but just carry on making the mistake, I guess until one day finally the right pattern gets learned through sheer brute force of repetition. In the meantime, they're perfectly well understood by everyone anyway.
Obviously as an adult you can somewhat shortcut this because of better understanding of grammar and knowing how to learn, and being quicker to absorb and make the changes, but regardless I think the basic premise still applies - you learn the right way over time just by doing it over and over and over until you can't not remember it is the right way.
And, to be honest, if the wrong way is understood, how practically wrong really is it? (you will always always have tells you are not a native speaker no matter what, some of these can even be charming, I don't know if it should even be a goal to get this to zero at all).