Honestly, this game is really, really mature. I actually found some of the non-sexual scenes to be the most disturbing (e.g. torture, mutilation, public execution, certain obscenities, ect.) I think that it is possible to avoid all nudity, and I'll give you a guide to do so, but first I would like to say that the game is SO much better when you just play the game, rather than play it while trying to avoid mature content. I'd reccomend waiting another two or three years, but here goes..
First, there are two non-avoidable nude scenes, both near the end of the game. One utilizes a wierd, comic-book style art that you will have seen on occasion by then, and onother is in the epilogue, that featuress some half-naked women in a still shot with rotating camera.(you will also have seen this used twice by then) niether of these scenes is sensual at all, and merely serve as background while geralt and dandelion narrate, respectively.
Don't pick "That morning, the king summoned me" during the interrogation in the beginning of the game.(not that bad actually, just close your eyes and count to ten after geral turns to the girl in bed with him.
In the prologue, let Aryan LaValette live. If you don't a brief but very non-sexual bit of nudity comes up at the end of the prologue.
In chapter one, don't go to the whorehouse beneath the inn(obviously).
In chapter one, in elven ruins, don't pick the "You could use a bath" option.
At the end of chapter one, you are given a choice between siding with two different factions (Scoi'atael and Blue Stripes) Choose to side with Vernon Roche, and the Blue stripes.
In chapter two, don't go to the brothel. one quest involving square coins requires you to, and that one's okay, but just don't employ the prostitutes. I think that part is obvious.
Other than that, don't get into a romance with Ves.
In chapter 3, don't flirt with Cynthia.
Mostly, just use your head. If someone offers you a "fun time" or to "repay you for helping me", say no. It's generally obvious when sex is about to happen.
Okay, I think that's it, but remember, this is a choice-based game, so there are hundreds of different ways that the story could play out, so this guide is by no means fool-proof.
As for alternative games, Try Dragon Age series if you're okay with old graphics and meh combat. Mass Effect trilogy is fantastic if you like sci-fie or cover shooters.
Sorry that a "quick question" got such a long answer, but I wanted to be thorough. Hope this helps!