An individual who has not reached puberty is called prepubescent. Can we call them a "minor"? Or can we call them 'non-adult'? Note that, we are not referring to their legal right, but only physical strength for sexuality is meant in the context. Such as:
i. A prepubescent can't make a child.
ii. A minor can't make a child.
iii. A non-adult can't make a child.
Problem with the last two is that a person who is under the age of 18 can still make a child though.