Which person has zach been friends with the longest?
SELECT T1.age FROM Person AS T1 JOIN PersonFriend AS T2 ON T1.name   =   T2.friend WHERE T2.name  =   'Zach' AND T2.year   =    ( SELECT max ( YEAR )  FROM PersonFriend WHERE name  =   'Zach' ) 
person Zach has been friends with the longest refers to MAX(year) in a relationship table;