I work in a bar myself. I dont mean to downplay what you may be hoping for or your friends were saying but...
No matter how old you are, you HAVE to be carded. At my work, we recently got in a lot of trouble for not carding a 38 year old. **** happens, and you think someone is old enough but you have to card them no matter what. If someone was to get in an accident after they left the bar, you're looking at losing your license for serving someone without ID.
About the girl, with the girls I work with, they use sex to get those good tips. They flirt, play, have fun, talk and go out of their way to make the guy customers think they're into them. Give out a phone number (fake of course....can be fun to give our manager's number though
and the guy will almost always drop down a huge tip. That is why us guys have problems getting tips...sure, we can sweet talk and make the ladies happy....