You'll love it here. Do some good research on the forum and other places to make sure you bring enough money to cover your costs (or you won't love it here - don't know if you're getting paid, but even if so, I wouldn't think it would be much for an internship) and you'll probably have the wildest time of your life. Make sure you know about the difficulties of getting money here if you will need to (you don't want to depend on debit or credit card - you lose maybe 25-30% of your money here that way) and think about bringing as much with you as you can if you have a safe place to put it where you're staying. Apartments often have safes, maybe hostels as well.
You can find a party probably any night of the week, but particularly Thursday through Saturday. Parties don't usually start until after midnight or later and often go on until 7 AM, although pre-parties [previas] may start a little earlier, and often everyone ends up going dancing and/or drinking in a public spot - starting around 3AM maybe.
A decent-looking foreign guy from just about anywhere will probably have girls waiting in line.
That seems to me to be the social life of someone your age, here. I've got two girls a bit younger than you (the oldest in her second year of university) and one who will soon be of the age to want to party (I dread the moment) and that's pretty much how they see things.