during my visit in 2014 my friend and I decided what better thing to do after dinner would be to go and do a little dancing. We tried a few places, but, alas, we aren't 20 years old any longer... Most of these places don't start hopping until way past my bedtime. Now I'm not that old (yet) but I'd love to find a place that has a DJ or something around 9 pm. By midnight we're generally looking to head back home. We tried a nice outdoor venue across from the hardrock (the name escapes me). We were there almost every evening and often the only ones there, except for Thursday night. I don't know if there was something magical about Thursday, but it was what we were looking for unfortunately on our last night there with an early flight the next morning...
Bugaloe on the pier on Tuesday nights has a band. They usually get people up and dancing but really depends on the crowd. They are a good band for it though. Moomba on Sunday may start around the time frame you are looking for, they have a band first then a DJ for the later crowd.
I don't know if it is still opened but there used to be a club called HIPSZ. Also you may want to try Gusto Night Club Aruba. The crowd gets younger later in the
night when you are ready to pack it in.