Oka is a nice one. Accessible by car, then a 20 minute walk past a sandy/swampy/forest-type area. Or direct by boat.
Crowd: all kinds, from 20 year olds (both bikini wearing or naked), to 70 year old naked guys and girls. Most seem in the 35 to 55 age range.
Beach itself: very nice. "Public Oka" is over-crowded. "Nude Oka" is pristine, and has a very low density of people. It's about 4 Km long!
But the girls are definitely hotter on the "bikini" side of the beach.