How can i model the age of schema.org/person in rdf?

Question

I have the following task to solve:

Model the following sentences in RDF (Turtle). If possible use URI from schemas available at schema.org or GoodRelations:

Jonas and Rosemary are children of Peter, who are 3 and 5

So i defined the following already:

@prefix schema: <http://schema.org/> .
@prefix ex: <http://example.com/> .

ex:peter a schema:Person .
ex:jonas a schema:Person;
         schema:children ex:peter .
ex:rosemary schema:Person;
         schema:children ex:peter .

It appears that age does not exist in schema.org. Is there a way of modelling it with birthDate?