Welcome to the forum, drps4.
Wherever you are in the USA, there's certain to be a school or college nearby running courses for people like you.
The standard of your writing is not bad at all. Here are a few corrections:
I arrived in the United States as an adult and have lived here for 17 years. Now I'm in my 40s. I speak English but not fluently, and I'd like to improve my English in reading/writing/speaking. My ultimate goal is to read online articles and novels and speak English fluently.
I don't know if this information is enough for you to judge my English level but I think it might give you a little idea.
I honestly don't know how to and where to start. Any recommendation of how to start studying? Any suggestion of books/novels/websites?
Thanks in advance for any help.
BTW, correct any of the above sentences if I'm wrong.
Interested in Language