A friend of mine's daughter has glasses and she is 5. We've had Wolf quick screened and it looks like he needs to go in for a more in depth screening soon. 4.5 is definitely not too young to check. Many optomitrists will do cheap or free quick screens for the little ones. I have very bad vision and it was not caught till I was in 3rd grade and having horrible headaches because I was capable enough to compensate at school.