No, pretty much everybody is able to acquire another language unless they have a neurological disorder that makes them unable to acquire any language at all.

You don't need to be young or be a child to acquire a language either. The critical period hypothesis is a causation-correlation fallacy at best. It points out many issues directly related to traditional language learning methods and not acquisition of another language at an older age; the issues it points out are the resultant bad pronunciation, spelling errors, grammatical errors upon trying to output etc.

These do not result from "improper age" or "an inability to learn another language", they result from how society as a whole has accepted "formal study" and "language courses" as the best ways to acquire a language, which they are definitely not.

Language acquisition is achieved first and foremost by comprehensible input in the target language. Hundreds and thousands of hours of comprehensible input. This can consist of any type of content a person enjoys watching, as long as it's language dense, easy to understand at the start and slowly harder going forward. A good figure to aim for is 10,000 hours of this.

Production of language, or output, is not beneficial to the learner, especially at the first few thousands of hours where it can permanently damage the learner's ability. The reason for early outputting being so detrimental to language acquisition is that as the learner doesn't yet completely know how the target language sounds, and they don't understand grammar rules intuitively yet because of the lack of input, anything they force out will in all likelihood be incorrect and they will unconsciously reinforce the incorrect grammar and pronunciation they just outputted.

So the best way to get to fluency is by doing as much input as possible and while starting out as much no output as possible. This is also usually called immersion learning.

You did mention immersion in your text, but considering that you live in an English speaking country you most definitely were forced to output early to at least survive, which damaged your speaking skills. The reason your reading may be bad is that you may not be reading enough English. If you're talking about language courses when you say “formal study“ and not just skimming through a grammar textbook for an easier time with immersion, which you most likely are, that may have harmed your perception of how English sounds too due to toxic input (the incorrect speech/writing of other learners).

Tatsumoto‘s website is pretty useful for more information and resources on input-based learning. It is primarily for Japanese but as language acquisition doesn‘t differ from one language to another it doesn‘t matter and you can just skip the Kanji-specific parts. I would just think twice about joining their community though as they are pieces of shit, but the website is really well made for a complete language acquisition guide that only uses Libre tooling.

Edit: The amount of misinformation in this thread is just sad. I reached basic English fluency at around 14 and I'm currently doing Japanese immersion, with my comprehension rate of the Japanese content I consume being around 90%. And I'm not 9 months old, as you can also probably tell.

Edit 2: I forgot about Antimoon's Learner Reports. Antimoon as a source is a bit outdated, but they have some interesting stuff in there as well.