Okay-- this sounds exactly like me starting around that age and continuing in a more conservative manner well into adulthood. I would become so overstimulated by what I was reading that I would immerse myself in a fantasy world replete with my own details. Real life was "drag" compared to what I could mentally construct from a book. It could completely explain the impatience with the grind of daily life for a highly imaginative child.
Here is what worked for me-- my family had a mini trampoline. I would bounce and think-- sometimes putting on some music. The advantage was that the mental overstimulation would wane once my body became tired. The trampoline was gradually replaced by long walks, then eventually a strong running regimen (complete with headphones to screen out real world distractions). I found in my case that there was a heavy connection with mental and physical over excitability. Intense, short amounts of exercise (alone) helped with the balance.
I am in mid forties and can still still get overstimulated by a good book or interesting thought. Because my physical energy is diminishing- pacing the floor or periods of silent contemplation work now.
