When it happens is different for every child. It may take a few days, weeks, months, or even years. This is normal . Most boys will be able to retract their foreskins by the time they are 18 years old. Some foreskins retract soon after birth.
Separation can even occur before birth, but it is rare.
As a boy becomes more aware of his body, he will most likely discover how to retract his own foreskin. Sometimes the foreskin will puff out, like a balloon, while a boy urinates. This is normal and is a sign that the foreskin and the glans have begun to separate from each other. The normality of ballooning is seldom admitted. Foreskin retraction should never be forced.