Mentorship is considered very important in professional growth. But the confusion here is that people would always think a mentor should be older or higher in rank than and of the same gender with the mentee/protege.
First of all, we need to understand the definition of a mentor as most people confuse mentor-ship with coaching or financial partner.
If the definition of a mentor is someone who helps you grow professionally by devoting time periodically to assess your growth, put you in line where you default and allows you to bother him with issues that worry you a lot. Then the person needs a coach and for professional purposes it's better to have a coach of same gender so as to avoid abuses of trust. But then, abuses can happen with coaches and students of opposite gender as well. So in my opinion , better a coach you trust and is higher in level and experience .
If by definition of a mentor you mean someone that helps you progress financially by giving you tips on how to make more money and stabilize financially, someone who will give you the courage and the will to break out of poverty, have great investments and launch you into financial prosperity. Then you need a financial partner or financial adviser. It can be a colleague , your spouse , your boss or even a friend. This person can be of any gender , can be older than you or younger so far the expertise is there and the solutions proffered to you is working.
In my opinion, a mentor is a role model. Someone who has passed through the stages of coaching and financial advisory role. Someone who may not have the chance to teach you in details but is someone you would love to be like when you grow older. You read them and their articles on how they made it. You can chat them up once in a while and get one or two motivations from them. These are your mentors. They are the finished product of what you anticipate to look like or become when the deal i done.
In some cultures a mentor/mentee relationship between different sexes would be forbidden unless it is also a parent/child or brother/sister relationship. The confusion comes when someone from another culture isn't aware of such restrictions. Also, in many contexts, the default assumption would be that mentors are male.*
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* Here's a riddle whose puzzlement depends on this default assumption: A man and his son are in a terrible accident and are rushed to the hospital in critical care. The doctor looks at the boy and exclaims "I can't operate on this boy, he's my son!" How could this be?
Karl Pfeifer I understand your clarification on the cross-cultural issues regarding to gender considerations in mentor-mentee relationship. That is right. Then if culture does not restrict such, must it be that the mentor and the protegee should be of same sex?
The mentor gains nothing in monetary or emotional terms, but keeps their distance. Purely altruistic. If you seek to gain, you merely seek disappointment.