For Exotropia there is no right age. It actually is dependant on three criteria. Based on the following criteria the age can range from very young to middle age.
Is the squint present for more than 50% of the waking hours. If it is then we need to perform surgery
The squint may not be present for 50% of waking hours, but if the child is complaining of headaches or eyestrain then squint surgery may be the answer.
Let me explain a bit here. Basically the child is very good at controlling the squint. so the squint is not visible much. But this constant control that the child is exerting is like lifting weights and if one were to lift weights for the whole day there will be pain. Thus the child complains of pain or headaches or eyestrain.
Cosmetic appearance would be the third reason to correct squint.