Okay, I think he would love that: someone with an open mind who gets excited by his magical whimsy and appreciates even the simplest spells and tricks he shows them.
It makes him feel proud when he can do the silliest things and get such enthusiastic responses - making items bigger or larger, making things float or zoom around the room, turning everyday items into big, buoyant bubbles or blooms of colourful flowers.
Solomon promises that with a little time and patience, even teen!MC can hold the wonders of the world in their hands like he can. They open their palm and he conjures twinkling stars or puffs of snow or even little dancing flames they can see and touch (nothing that could hurt them, of course).
Solomon likes to make teen!MC laugh with delight whenever he performs one of his charming antics. He enchants their pen so that it sings and cheers in a high-pitched voice while they do homework. Lucifer throws a fit when a little storm cloud follows him around the school and rains on him every time he says or does something mean.
Solomon gets teen!MC all the books about magic he thinks they might like to read, and he gets them their own wand (it looks so much like a toy but he proves it's quite capable of the most potent spells). He even debates getting them their own little apprentice uniform with a coat similar to his own.
But it's not just about silly magic and parlour tricks.
Does Solomon see teen!MC as his little sibling? The child he might never have? No one's really sure, but what they do know is that he adores them. Teen!MC couldn't ask for a better teacher or guardian - so long as they don't eat too much of his cooking.