Ask yourself what is a succubus and what results do I want out of the character and plot?
First, let's do a bit of research:
The Modern version
The modern version of a succubus is completely different than the originals. The modern version is a cute or otherwise attractive female with or without horns, wings, and a tail, which is extremely lacking in morals, and possibly requires intimate activities or side-effects in order to survive. The more dangerous versions drain life-force or some other vital requirement for life. They may or may not be considered "evil", which is a complete departure from the original.
The original versions
The various original versions come from Babylon, Sumeria, Arabia, and Mesopotamia. They were later incorporated into Hebrew mythology and from there into Christian mythology. Most versions were night demons, often with partial or complete bird-like characteristics: such as clawed bird feet and wings, and they were almost always mentioned in conjunction with other bird-like beasts or demons. They were often classified as a type of demon known as a 'lillin'.
They were hideously ugly with sharp claws and could not stand upright, being forced by their warped and twisted bodies to crawl on the ground. Notably unique, the Arabian version was a sub-class of Djinn, and wandered the wastes and deserts. All versions of them were irredeemably and unapologetically evil.
Almost all original stories regarding these creatures involve one of two themes: seducing males and forcing themselves upon them in order to forcibly steal their seed, OR kidnapping and murdering (sometimes devouring) young children, especially newborns. Oddly, it seems one or the other, the stories never mix the two themes, at least none that I have found. Some ancient cultures would even make warding talismans which were worn by babies until they were too old to attract the demons.
As demons and devils are incapable of reproduction, a succubus would steal the seed of a human male through rape, pass it to an incubus (the male version) via intimacy, after which the now corrupted and tainted seed would be passed to a human female, again via rape, and the resulting offspring of the human woman would become a 'cambion'.
As a side note, there are theories that these stories were originally invented as an attempt to explain sleep paralysis and nocturnal emissions.
What do you want?
As we have covered, the major themes of the original succubus were evil, seduction, rape, theft, death, and hunger. Lust was not part of the succubus theme as men and women alike were horrified and traumatized to be raped by these demons; the lust angle was a modern addition after they stopped being ugly and deformed.
Is PG-13 tame enough for Young Adult fiction?
In any case, as you have stated, you want a lust-themed succubus, that is tame enough to fit PG-13. Considering that there are PG rated media which contains nudity and even nude sex scenes in PG-13 movies, I think you'll need to be a trifle more specific in what is and isn't going to be allowed.
I will make some assumptions and go with no nudity or sex?
Since 'lust' is going to be the major theme, let's ask the obvious question: What is lust?
At it's core, lust is selfishness expressed through possessive and unrestrained desire. Lust places what you want to have, possess, or control above what anyone else wants. This is why it is actually a form of selfishness. After all, one can lust for power, for money, for a car or boat or house, for going somewhere, for doing something, for doing something with someone or even for the person themselves. In modern times, the term lust has acquired a sexual sub-theme.
This gives us some new themes to work with.
The new, more tame, incarnation of lust
As we have reviewed, other than sexually oriented, a lustful person could be controlling, they could be possessive, and they could be selfish. A lustful person could be forceful, inconsiderate of other's feelings and desires, as their own lusts are obviously more important. What they lust after need not be sex, or sexuality, it could be an object, a person, an action, or even a location. Le'ts brainstorm some alternate versions of lust and what that might look like:
- Lust for a location: someone who lusts for a location would do everything in their power to travel to that location, and then stay there. They would do anything to get there, and woe betide the person who stands in their way, or who attempts to force them away. They might decide to preserve the location exactly the way it was when they first saw it, violently reacting to anyone who attempts to change it. Possible characters: terrorist against a land developer, a murderer who targets people who litter in a park, a preservationist or expert restorer of old buildings.
- Lust for money: someone who obsessively seeks to hoard money and other things worth a lot of money. Possible characters: a miser, an artifact hunter, someone who controls the banks of a certain neutral country.
- Lust for an object: someone who has a favorite object or type of objects and will do anything they can to obtain them. Possible characters: an anime figurine collector, a bibliophile librarian (woe betide those who return a damaged book or are late) or book collector, a car collector.
Something old, something new
Finally, we can touch upon a toned down version of the more stereotypical succubus: someone who either lusts after a person, category of person, or an activity with a person.
- A person who lusts after a person may take the form of an obsessive girlfriend, relative, friend, or just the girl-next-door who can't stand anyone getting close to the person of their focus. An example of this might be Jeremy's little sister from Phineas and Ferb, who can't stand any girl getting close to her brother.
- Another option involving category of person could be the girl who has to have the attention of all the boys, no matter what, and no matter who they are with or what they are doing. She expects all men to pay homage to her the instant she walks in the room. Anyone who fails to do so earns her ire.
- Finally, a person who lusts after a particular activity could take the form of someone obsessed with holding onto the hand or arm of the person of their focus, or cuddling, or even riding upon their shoulders. Should you prefer the ultra-traditional version of actual intimacy, then kissing or simply implying that they are going off-stage to do "that" could meet the goal.
In conclusion, be creative and open-minded as to how one defines 'lust', as well as how and what one can obsesses over, and I believe that you will find many possible options available.