Ask HN: How do I ask someone senior to me to be my mentor?

I lead a forward-thinking technology delivery group within an otherwise stodgy enterprise. The group Chief Digital Officer (very senior) and I share the same thinking (CI/CD, SaaS, MVP, etc) in how to deliver software within this enterprise.

We've met in a formal setting and I think I made a good impression on him. We've both been with the firm a short time. I sent him an email after we met saying I was happy to meet him, he responded with the same and told me to stop by whenever.

I've never had a mentor before and think he would be a terrific mentor for me, and I a terrific mentee for him.

What steps should I take that will give me the best chance of forming this formal mentor/mentee relationship?