It sounds to me like the age regression you want to engage in is pretty "non-sexual". I mean, there might or might not be a part of it that is a turn-on, but you don't want to do overtly sexy stuff while acting like a six-year-old.

I wonder if this is clear to him, or if the phrase age-play is confusing to him. What about if you tell him you just want to pretend to be a little girl cuddled up with a safe adult? I'd leave any mention of Daddy out of it for now, and also of spanking. But a pajama party watching Disney movies and eating cookies might be OK with him. Once he's experienced that, then maybe next time he can tuck you into bed and give you a kiss goodnight.

I would suggest leaving all sexy stuff and all discipline out of it until he's very comfortable.