"Lust is to the other passions what the nervous fluid is to life; it supports them all, lends strength to them all ambition, cruelty, avarice, revenge, are all founded on lust." - Marquis de Sade
When Sebastian stops to think about it (which is never, because unlike the inferior little creatures that are humans, he can think and walk at the same time) Ciel had been both too young and too old when the demon made a contract with him.
Too young because it was obvious to see just how naive and ignorant he was (which can also be said about the older, more jaded Ciel, though perhaps not quite as much), only a child and yet not in the most significant of ways. He was too young for Sebastian's tastes (though not for other demons'), not yet acquainted with self-corruption and moral rot and denial, though smelling of pain and desperation from a mile away.
When Sebastian first met him, Ciel was nauseatingly untouched by the (dirty greedy savage) ways of the world, and the demon still cannot say what his soul tastes like (although he did get a lick of it when the contract snapped into place, like a small bite of a twelve-course dinner that is supposed to last him until the clock strikes midnight), but he hazards it is something between unripe wax cherries and cocoa powder, sour enough to hurt and dry enough to choke to death on.
When Sebastian first met him, Ciel was too old for the demon's preferences. Too old to be molded easily into the kind of undemanding but delicious meal that Sebastian preferred (which proves itself to be not as much of a downside as the demon comes to realize just how rich stubbornness tastes and how satiating contempt feels in his stomach). So maybe Ciel was not too old for Sebastian to enjoy, after all.
Really, the little lord is as much of a contradiction as he is a certainty - his soul belongs to Sebastian, inside Sebastian, but when that will happen and how the child's essence will actually taste is a mystery he both wants and dreads to solve. Some days, the demon finds the young boy with an old soul (an old soul covered in layer over layer of exquisite torment that tempts Sebastian like no chocolate cake or roasted beast ever has) so entertaining he is tempted to revoke the contract and simply spend the rest of the human's pathetically short lifetime just watching the young master stumbling and scheming and charming his way through life. But Sebastian is no fool - prey is prey, and even he tires of playing with his food. (And yet he cannot help but see his lord as one of those sweet confections so pretty that people would rather let them spoil than eat them. Good thing Sebastian has already spoiled Ciel rotten, then.)
But, in the end, even if the child were to gouge out the eye marred by the contract, it would not nullify their bargain, nor would it stop the demon from taking what rightfully belongs to him - by force. But, oh, how much fun he would have luring that appetizingly recalcitrant soul out of its vessel, fighting it and hurting it and deceiving it until it comes to him willingly, like a young lamb to slaughter.
And when Sebastian finally gets to ravage that small and lithe body, the demon's part of the bargain complete and the human's just beginning, when he can finally push the boy down onto the starched bed sheets and overstuffed pillows, climb onto the bed after his young master and kiss and bite and suckle on pale pink lips and moonlight white skin and bruise them purple and blue, swallow the child's whimpers, when he can finally lick and finger and thrust his way inside the small body and feel it give underneath him, he will be sure to savor the rich taste of victory (and when his teeth pierce that smooth skin and suck the corrupted soul within and greedily devour it whole, there will be a smile on his face, mark his words). The demon can almost taste it on his tongue, sour cherries and dark chocolate, the matured nuances of almost a decade spent in innocence and a handful of years spent in the company of humans so lowly you could almost think them demons.
And when Sebastian finally gets to lick his teeth clean of the last of Ciel's soul, there will be only a momentarily sense of regret, of disappointment at the fact that such a feast lasted so little, gone before it even began, and then the demon would revert to his original form, all pointed heels and suspicious shadows and danger, and return to hell, maybe come back to the surface every once in a while to search the human world for a tasty snack, as though there never were a young child with tempest-blue eyes and moonstone tainted hair and a soul that tasted more like temptation and broken dreams than hell itself.
(And yet Sebastian can't help but feel that that something's not quite right, that he's forgotten something, something crucial but not exactly important, not in the classic sense of the word. It unnerves him, this not knowing, and that, in turn, irritates him, which makes his double edged words even sharper than usual, and Ciel starts to look at him strangely, as though Sebastian is an old dog that has done something unexpected but not necessarily unwanted, and that that makes the feeling of wrongness even stronger.)
