Sex ('congress' if you want to use the poetic phrase often used in the Kingdom) is taken as an important part of life. At the same time people have a more matter-of-fact point of view of sex than in the present day. Certainly most folks don't associate a lot of guilt with sex. At the same time, no one would consider it to be trivial because it can carry magical, emotional, and physical significance at some level. That doesn't mean that some folks won't be more prudish, and some religions frown on some forms of congress, or congress under certain circumstances, and many use celibacy as a form of geas for their initiates or priests to show devotion to the god, or for ritual purposes. On the other side, many seasonal festivals feature outdoor congress ("Honest, honey -- it's just to make sure the crops grow up right."). The Nobility is, as a rule, less reserved than the commons, as the city-folk are usually less reserved than country folk. The Kingdom's culture does not include a great deal of body modesty (i.e. with respect to nudity). Mixed social bathing (usually excluding teens) is very common. While you aren't likely to see folks parading down the street in their birthday suits, it would not excite a scandal -- more like curiosity. Women in the northern part of the Kingdom will usually signal being "unavailable" (or at least generally uninterested) by wearing their hair up, while in the south hair under a scarf means the same thing.
For various reasons, pubescent Children (see here) are strongly discouraged from engaging in intercourse, but they aren't prohibited (in fact they are quietly encouraged) in exploratory "messing around" short of that. Demi-Adults are not discouraged from experimentation with intercourse, but are strongly discouraged from getting themselves (or others) pregnant, since that constitutes a responsibility that extends long after the new parent's 21st birthday.
One of the cults of the Western Pantheon, Taira (the women's mystery cult) has a wonderful little 1 point 'Battlemagic' spell called Misconception. The spell acts as a (fairly) reliable form of birth control, as well as helping to combat most sexually transmitted diseases. For obvious reasons, most women join the cult as Lay Members at puberty. There are other 'back up' methods of dealing with birth control and diseases -- primarily herbal in nature.
Prostitution tends to be legal, regulated (and taxed) on a local level. The common scheme in cities is to have an established 'Licensed Quarter' where that (and all other 'disturbing') entertainment may take place. In Tara, visit the lovely 'Street of Dreams'. In Tyre, it would be the 'Street of Red Lanterns'. Common prostitutes (whether working the streets or inside brothels) must practice their trades entirely within the Licensed Quarter. A licensed Geisha (male: Geisho) may attend to assignments outside the Licensed Quarter, but is not permitted to solicit for further work there and are expected to maintain a certain degree of discretion and deportment. Registered Courtesans are pretty much above all these regulations. These distinctions represent degrees of increased social standing as well as also having formal training in the 'vertical' entertainment arts.