Advice request: How to best build a relationship with senior mentor

Hello everyone,

I am currently finishing my undergraduate, and in September I will join a commercial bank in the risk division.

2 weeks ago the IBD society hosted an event on campus with the COO of such bank; I took the chance to speak with him and got his business card.

I would like to keep in contact/build a relationship with this person, so that when I actually start the job in September he could be my mentor

I would like to have a bit of advice on how to address this, as it is the first time that I do something like this and I'd like to not spoil it.

I still haven't written him anything.

Some issues that I thought about:

-What to write in the first email? -How to keep the relationship going during the summer up until I start ? -I also wondered whether he could be a good mentor or not - he is a the highest level in the company, while I will start as a graduate. Maybe a "closer" mentor could benefit me more?

I waited 2 weeks since the event, and I know that this is probably a mistake, but I just thought that keeping the correspondence a bit distant in time would allow to keep this going until September.

Any ideas?

Thanks