Student or Learner
Isn't it about time you got your hair cut?
What does it mean?
***Neither a teacher nor a native-speaker***
It is about time:It is a idiom that means "You did the right thing, actually you should have done it by now."
So your sentence means that you should have your hair cut (implying that you should have had it cut some time ago)
The short answer:
Your hair is too long.