There is a 1864 record of a NY Naval Enlistment of John Wolfe, age 22 b. IRE but without more details about your grandfather it would be extremely difficult to determine if this is the correct man.
United States, Naval Enlistment Rendezvous, 1855-1891
age: 22 est birth 1842 birthplace: Ireland
place of enlistment: New York
month and year of enlistment: Apr 1864