Hi, I've been to Croatia at end-June this year. If you really like isolation and secluded beaches where you can do (almost) everything on the beach without being bothered and/or seen, I can recommend the southern side of the island of Hvar. I (we) went to a very isolated village called Zavala. To get there, you have to drive through a very narrow and dark tunnel of about 1.2 miles. There only space for one car and the access is based on a sensor traffic light.
The waters are fantastic, the nature is practically unspoiled and you can go snorkeling, diving, windsurfing and, of course, you can practice other “sports” right on the beach. There is a small portion of pebble beach, but most of it is rocky. The best part is that you can very easily hide behind those rocks and do whatever you like. However, don’t let yourself completely away and always keep an eye on the waters. There are lots of swimmers and you don’t want to get caught in the middle of the action.
Or do ya?
Oh, I forgot, most of the tourists are around 40, so if you want to see “fresh meat” I don’t think that’s the right place for you.
here is a photo: