Hmmm - yes you can't offer cheaper insurance to females but if the risk associated to a certain demographic (like old people) is lower then the insurance premium is lower!
If statistics state that females aged 20-25 in Bristol are less likely to be in an accident than males aged 20-25 in Leeds then the female will have the lower premium and in general, women and old people are less likely to be in an accident..... they cause many but are never involved...haha - joke!!
JJ