Hi Laura Jane,My girlfriend and I are both 20, so could be the youngst people that have been to Plakias on this forum. We have just returned from are first 2 weeks there last tuesday and loved it.
Bars i recommend for young people are: as mentioned the bar above Ostraco called the Balcony bar. Here they play music videos on a big screen, the music is ok Michael Jackson and some new UK chart music etc. The best time to go there is the weekends, it can get really busy then, this is when alot of the greeks go there also. It can have a good atmosphere. Another good thing about this bar is that you can sit out on the balcony and look down on the main street below and watch the world go round!
Theres also a good sit down bar up the road abit from balcony bar. Cant remember the name of it. Its next door to a car hire place and opposite the car park where the coach will drop you off. here they have funky seats and also play english music.
Enjoy