Our boys (9,7) read their Bibles every morning during the time that my husband and I read ours. They read the King James Version and understand it.
Right-away-in-the-morning Bible reading has been my personal habit since I was 12. To continue with this when we started having babies (four of them), I had the little guy sit with a basket of baby books when he was around a year. It started out with just a few minutes, and worked up to the whole hour of my Bible reading. When ds#2 came along and got old enough, he joined the other side of the basket. Training them to be quiet and look at books takes some time, and at times seems unfruitful, BUT IT IS SO WORTH IT.
Now we have four children (9,7,5,3) and they all sit (mostly) quietly on their own beds reading Bibles and books while I sit on my bed reading my Bible.
When our oldest got to where he could read well enough (around 7) he wanted to start reading his Bible that someone had given him. I worked out a bookmark of 10-12 vs passages in Luke for him to work through. Then, I think he did Joshua, and after that, he wanted to start in on Gen to the end. After 2 full years of reading his Bible (first for 5 min, then 10, then 15, and now 20 min each morning), he finished the whole Bible! After that, he started over, just like my dh and I do.
Ds7 is now doing the same thing.
I’d encourage you to get a specific time each day, and it is so much better if it is before everything gets going.
He’s going to wane in his “excitement” but that’s life. Keep at it!
Hope our experience is helpful to you.