@MushroomI agree with 'fourth-grade' and would, in fact, put that at a minimum of fifth to sixth in 'reading score' level and high school at least in terms of thoughts and ideas. I'm prone to characters who wax philosophical and think about things (a lot) and my ideal reader follows that.
I agree with Mushroom about sex scenes. The sex is important because it's another important character interaction, not because it's hot people getting it on. I don't find sex scenes interesting to write, or read, when they're between people who have an established relationship unless something new and different and interesting is happening, either physically or emotionally or on whatever level.
Also, someone who wants to go on an extended journey with the characters. I'm telling a long story; hopefully people are willing to join me on the trip and enjoy the parts that are quiet and 'normal' as well as the parts that are action and drama.
So, really, my ideal reader is probably myself first and then people more-or-less like myself. As I receive reader feedback, my understanding of who my readers are grows, but that's not an 'ideal', that's reality.
Part of the analysis, I think, are the readers who are decidedly not ideal. Like most people, I like to be liked, and the notes from people who just plain don't like the story were hard to take. Not critical notes from someone who's involved and interested and doesn't like a direction the story went - those are highly valuable. But the occasional reader who says something like "Slow?! Paint dries faster!".
That's perfectly valid from some perspectives, and I had to be willing to say, hey, if it's not your cup of tea, go read something that is. I can't please everyone, and my ideal reader (me, again) wouldn't like it if I tried to turn things into an action-packed page-turner where the interesting character moments were shoved to the side.