"Sa fille est une adolescente."
Translation:His daughter is a teenager.
It's the same sentence! When talking about possesion, the gender of the possesive term (sa/son) depends on that of what is owned. For example, son frère and sa sœur could both mean either his/her brother and his/her sister. The only exception is when the object begins with a vowel, which is when it will always be masucline (for the sake of pronunciation). So we'd always say son ami AND son amie, instead of sa amie or s'amie.