I was advised to read 'Insight' when I was 21.
It took until I was 45, 24 years, and I had to learn a great deal along the way just to get past successive pages. His writing was difficult for this young man to follow, largely because his words and concepts were far too difficult for me. I had to read and understand many, many other books just to grasp his meaning and to move on to the next passage on the page.
He is the only man I have heard of (and read, and read of) who has written a fully logical proof of the existence and the attributes of God.
His book sits on my shelf.