The link given below should give you some idea as well.
http://sqlhints.com/2015/07/10/how-to-get-difference-between-two-dates-in-years-months-and-days-in-sql-server/
How to post data/code on a forum to get the best help - Jeff Moden
http://www.sqlservercentral.com/articles/Best+Practices/61537/