Hi G.! My daughter started complaining of headaches about the same age. I to thought she was only repeating it because she heard mommy say it so much. In 2nd grade (almost 5 years later) the school gave her an eye exam and we found out that she needed glasses. Within weeks of getting her new glasses she stopped complaining about the headaches. I can't help thinking that I could have done something about it sooner and maybe her eyesight would not be as bad as it is today if I had her eyes checked sooner.
Another cause for headaches in children can be bladder infections. Often time kids will hold their urine to long, or not release all their urine when the go to the bathroom. This causes a bacteria build up in the bladder and infections. Sometimes, especially in little boys, the only symptom is a headache.
I know how you feel, and I would hate for you to make the same mistakes I did. It is worth a trip to the doctor, just to be safe. I hope everything works out for you and your little boy!