A quick fix for this so-called "gender gap" - we should aim for all people to have say 15 years in retirement, based on average life expectancy (which for males is approximately 82 and females 84).
This means that the male "retirement age" should be 67 and for females, age 69.
Those extra years of SG contributions for females will compensate for the time off they may have had earlier in their careers, while supported by their partners and any maternity leave entitlements.