Premature ejaculation is when the male ejaculates quickly during sexual intercourse. (Absolutely nothing wrong with a woman who orgasms too quickly, double standards no?) Sometimes this occurs before penetration or soon afterwards. 

Some facts about intercourse
A landmark study published in the Journal of Sexual Medicine in 2008 found that the median length of intercourse was 5.4 minutes. Other studies have found medians of 7.5mins (these studies ignored foreplay) A poll carried out found that women believed that 11- 13minutes of foreplay with 7-8 minutes of intercourse was considered adequate.
According to a study of United states and Canadian sex therapists, sex that is too short lasts 1-2 minutes,adequate lasts 3-7 minutes and desirable is 7-13 minutes the range for too long went from 10-30 minutes. (Penetration only)

The Hard truth
Again sex should last as long as both partners require it to. You can increase the time of your pleasure by using Vigrx Plus. Premature ejaculation medically speaking is sex lasting less than 9-12mins. (Full-on-penetration minus the foreplay)