I know he's only a year old so nothing's set in stone and he's a bit young for any sort of orientation labeling really but aro!ace!Jack?
As much as I appreciate Jack’s lack of sexuality this season being due to Dabb and Berens treating him like the child he is, I certainly don’t see why he couldn’t also be aro/ace :)
There would be that awkward period where Jack has to learn for himself what it means to be aro/ace, where maybe Dean and Sam (with the best of outdated intentions) encourage him to talk to and flirt with the young waitress/waiter who winked at Jack, and Jack just not getting the subtext. Because he’s more interested in having a friend to talk to, and share secrets, and generally not feel as lonely as he sometimes does, and he doesn’t feel he can fill those needs strictly through sex or a romantic connection.
I’d like to think Cas would be in the best position to explain to Jack, that just because he sees humans dating and whatnot doesn’t make him abnormal or any less half-human for not copying them. That it’s okay not to be interested in someone just because they showed interest in you. That he’s not broken or lacking for having no interest in sex or romance, and that there’s plenty of relationships to be had in life without them.
(My only word of caution is that certain writers next season might think Jack is now at an appropriate age for some sort of pseudo-puberty, and that means he can start becoming interested in girls, because heteronormativity >.> Not to cause panic, but I am bracing myself for it)