There isn't"average" I am unaware of any population study of this. Safe drinking limits for men 21-60 are no more than 2 standard drinks per day (12 oz. Beer, 5 oz. Wine, 1 1/2 oz. 80 proof spirits), and no more than 4 drinks on one occasion. Amounts over that are associated with a number of health and behavioral issues, including increased hypertension and liver problems. For women and men over 60, 1 drink/day.
How much is too much. A male should generally drink no more than three alcoholic beverages on any one day (one 12 oz beer, 4 oz wine, 1 oz hard liquor) and no more than 14 drinks in a week. For a woman these numbers reduce to two drinks per day and no more than 7 per week. More than this can cause problems with the liver, heart, brain, and other organs over time.