Yes he has always had the star! And I remember it being mentioned that mages have a star in their eye whenever they use magic. I think it's just not that consistent, or depends? But that theory is actually interesting!
I th8nk it has more to do with the color. #0's r white stars while Shao's were black. I think thays whats unnatural abt them
Shao's were black is not normal its kinda like an abnormality, looking at what ibuki says its likely the cause for the students to turn "evil mages"
Has Solo always had stars in his eyes when he casts magic? How interesting, I wonder if his connection to the evil mages is closer. I wonder if his organization is actually the ones behind the kids being evil