It is okay for our attention span to change over time with the transitions in our life. It is okay if you cannot read a book at stretch or watch tv. As you grew up, your priorities changed, maybe your energies are focused on other things, your job is based on a lot of screen time, you are used to more stimulating situations at work or home.. there could be a lot of reasons contributing to the issue you reported. Which is why you may feel exhausted when you may think of reading or watching TV to relax.
Next Steps
You may need relaxation time based on off screen activities.
Health Tips
Read 1 chapter at a time or only as much as you can.
Watch movie in breaks.
Develop other habits like going for a walk, home workout, listening to music or anything else that you prefer doing more now.