M_Boats: Do I need new sails

Hi I know this question has been asked before But can't recall the advise that was given. So here it is: I have a 1985 M15 for about 3 years and I just started noticing that the main hangs down about 4 inches at the back. Is this normal or are my 29 year old sails done for and I need new sails? Also where can I find out the sail dimensions for my 1985 M15 is there a web page somewhere ?? Thanks Klaas