I'm not sure 11 is really a flirty Doctor, he always seems quite uncomfortable in any kind of intimate situation other than with River, and even that seemed to take a while. He certainly doesn't have that "Hello girls," cockiness that Tennant had.
I think the next Doctor needs to be the right person at the right time for the job. Smith certainly wasn't my idea of who the next Doctor should be but he had me from "Do you have an apple?" (actually I think he kinda had me from his first interview when I decided he was a more than a little eccentric) So frankly I'll judge whoever the next Doctor is on their own merits, and if they choose a 25 year old south Asian woman who's as naturally the Doctor as Smith then better that to a 40 something white bloke who feels forced in the role.
That said I'm 99% sure the next Doctor will be both male, and older than Smith, in fact I think he'll be older than Smith is when he leaves rather than when he started. Mid thirties at least.