Will drinking moderate amounts of alcohol (500ml or less) twice a month, cause permanent ed?

Unlikely: It's unlikely that drinking 2x/month will lead to erectile dysfunction. However, moderate alcohol consumption is up to 2drinks/d in men and up to 1drink/d in women. 500mL = 17oz but 1 drink = 12oz beer = 8-9oz malt liquor = 5oz wine = 1.5oz 80proof spirits. Check out http://www.niaaa.nih.gov/alcohol-health/overview-alcohol-consumption/standard-drink. In general, ED is performance anxiety in 16yo