I don't see Jason x Artemis but if they are well written I don't have a problem with that. It can even be fun, it would be an odd couple.
If she call him "Little Boy" I don't see the problem. It's pretty normal in couples like "Bear", "Big Guy", "Tiger" even "Idiot" or "Foolish". Always with love.
I think is not for Jason's age. Only Artemis is too old. Or at least Lodbell said that.