[pan_w]

I think this is a great question. I don't think there is a definitive description for a mentor. It could mean many things to different people.

To me a mentor is someone who is interested in helping me, I have a good relationship with and cares about my growth.

How you two go about doing those things will be entirely up to you. For example, maybe you two have some frequency of checkins or interact on a need basis. This could be over plain old chatting, code review, or playing a game. As long as there are thought out topics to discuss and a medium that makes people comfortable.