You can get the year and month of the timestamp with YEAR and MONTH functions respectively:
SELECT from_unixtime(birthdate),FLOOR((YEAR(CURDATE())*12+MONTH(CURDATE()) -(YEAR(from_unixtime(birthdate))*12+MONTH(from_unixtime(birthdate)))) / 12) as age FROM `table1`
and here is sqlfiddle