I recently started working on sparql to generate query for getting the age of a specific person (say, Donald Trump)

The only thing I could understand is that it would be an instance of Person class. Can someone help me with what else needs to be done to get that specific information.

SELECT ?item WHERE {
  ?item wdt:P31 wd:Q5.
  SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
}