# Optional example
PREFIX info:        <http://somewhere/peopleInfo#>
PREFIX vcard:      <http://www.w3.org/2001/vcard-rdf/3.0#>

SELECT ?name ?age
WHERE 
{
    ?person vcard:FN  ?name .
    OPTIONAL { ?person info:age ?age . }
    FILTER ( !bound(?age) || ?age > 24 )
}