20-25 minutes is above average.
According to a 2008 study, the average sexual “experience” lasts from three-to-7 minutes.
Another 2005 study surveyed a total of 500 couples from five countries: the Netherlands, United Kingdom, Spain, Turkey, and the United States. The researchers found that the average time from the moment of penetration to ejaculation was 5.4 minutes.
In this 2007 study which surveyed 58 volunteers between 20 and 40 years old, the average ejaculation time during intercourse was 8.25 minutes.