Have you ever considered that when women negotiate a (typically) lower salary that instead of being less experienced and less aggressive as their male counterparts in terms of expectation and negotiation, they may be in fact be more realistic? More realistic about their own abilities, but also more realistic about the expectations of the job market and economic realities.
Research shows that men are more likely to overstate their abilities and ask for higher salaries that are not necessarily in line with their level of ability and experience, whereas women tend to only apply for roles where they feel that they meet all the selection criteria. This ‘inflation’ of salary expectations for men starts as early as the ‘reservation stage’ (the lowest wage you will take immediately after becoming unemployed) and continues once they get a job. Just then imagine how this inflation of expectations continues to flow through all aspects of that person’s career.
Food for thought.