"other" is redundant when you use "except". I would say "anyone" rather than "any girls" or "any other girls". You used the simple past - as a standalone sentence it's not impossible but I feel it needs extra information.
He never dated anyone except Jane at high school.
As a standalone sentence with no time marker (and assuming that you mean Jane is the only girlfriend he has ever had), I'd use the present perfect.
He has never dated anyone except Jane.
If you want to use "other", say "He has never dated anyone other than Jane".