for his/her age
El muchacho es alto para su edad.
The boy is tall for his age.
Es muy alto para su edad, ya mide un metro ochenta con trece años.
He is very tall for his age, already measuring one meter eighty at thirteen years old.
Estaba en excelente condición para su edad.
He was in excellent condition for his age.
Este chico sabe demasiado para su edad, es muy listo.
This boy knows too much for his age, he's very smart.
María se ve estupenda para su edad.
Maria looks great for her age.
He looks old for his age.
Mi sobrina es atractiva y madura para su edad.
My niece is attractive and mature for her age.
Su sobrina es atractiva y madura para su edad.
His niece is attractive and mature for her age.