"After reading half a page, you don't understand what you are talking about anymore?"
It happens to me if the language in the book is too difficult to understand, or if I am thinking about something. Or I simply "swallow" sentences, fragmentarily understanding the text.
I once read The Three Musketeers out of envy, it seemed that I was a fool and would skip such a book. In the end, I regret reading at all, because it's still boring.
I advise you to choose a genre that you like.
Or just find a list of books worth reading. Read 10-15 pages, if you liked it and want to learn more about the history of the heroes, then continue. If not, put aside the book and read it in a month / year, maybe some events will affect you or just solve problems, then the book will be better "digested".
Quite often they make films based on books. Watch just such a movie, if you liked it, then read the book. (sometimes they do the opposite, but I haven't read such books)
Sometimes design \ translation \ publisher plays a role, I like high-quality pages when sweaty fingers do not deform the paper (it starts to form waves), when the paper does not thin, beautiful cover and excellent translation. The same Hobbit, I have 2 books with different translations from the same publisher, 1 excellent, albeit not very pages, but 2 horror. A bunch of mistakes, a footnote under the term was stuck in the text, and not at the bottom of the page, the pictures are scary.
It also happens when books are written on computer games (mass effect, AC3), maybe worth reading, I don't know, but it's worth a try.
Or read in the evening / morning / afternoon for 20 minutes every day, get used to it and everything will be fine.
When "I read half a page and no longer understand what I mean" - this is the first sign that there is neither motivation nor interest to read this book. And this happens precisely because you "force" yourself.
And if you just have a desire, then it is never too late to learn. I would advise you to first choose something light, not in four volumes (that is, with War and Peace or Les Miserables, most likely you should not start) and be sure about what you really like and find interesting. After all, everyone has a hobby or hobby, try to find something from this section and read it.
You must also have motivation to increase interest. So why are you reading this book? (if you are not a simple reader). For example, because you really really want to understand this material or learn more about this or that era and its customs: from London Dickens to balls at Austen. There can be any motivation, even just a desire to show off knowledge in front of friends / girl / boyfriend.
In order not to be distracted by extraneous thoughts while reading, try to imagine (visualize) the plot. That is, you read and watch the movie in your head at the same time.
If we are talking about reading a textbook, scientific literature, you can understand what has been written by trying to slowly reread a complex sentence or paragraph over and over again, look in the dictionary for terms. Working in such a stressful mode for a while, you get used to it, and the process moves faster. If you find it difficult and uninteresting to read fiction, then it may be worth starting with a simpler text and gaining a reading experience that also contributes to a better understanding and assimilation of more complex literature.