My son is 7 years old and he started that a little over a year ago. He does it with both eyes. It almost looks like he's flirting. He sees a psychologist due to his mental challenges. I asked both Dr.'s and they said it was tics due to tourettes syndrome. They told me usually people with mental disabilities get it. I don't know if this helped but I thought I would let ya know. There is medication for this however, I'm not putting my son on it until it gets worse or he starts getting teased. They also told me it might go away for a couple months, then arise again. My son stopped for about a month, then started doing it again. It doesn't hurt them nor do they know their doing it unless you tell them. I've noticed the tics get worse when he gets nervous and/or stressed!!
You should arrange an appointment with his doctor, who will likely refer him to a neurologist. Most tics in children and adolescents are benign, but you should not assume that. He requires evaluation.