I have no advice, except to get older. I used to be terrible at concentrating. If there was a person in the same room, talking. I had zero concentration. Some people just need total silence.

I have to say that is gone now. But I compare myself at age 17 to age 33. You probably can't afford to wait 16 years.

A question of course is where the distractions come from. From outside, or from inside?

For your example of reading, I have that too for research papers sometimes. Your throughts just glaze over and you pass through the words without getting their meaning. I feel I have to stop myself and contemplate on the meaning of what I just read.

As for reading a novel, are you sure you are into the story? Or maybe it is too early to tell.

This is one of these things that are hard to comment on, similar to discipline. It is magically there, or not.
I like to think limiting distractions like a phone or computer, help. So by avoiding multitasking.. And that practice helps. But I am not sure.