Just a friendly letter to my ex-tutor

I am writing to my previous English tutor. I haven't met him in two years; recently he had tried several times to reach me through phone, though unfortunately I always missed his phone call. As college life would have it, I usually don't have a solid block of time to sit down and make a nice long phone call (not to mention the long distance bill...) so I decided to write a letter to him.

I have never written an English letter that's not for college application... so I'm pretty stumped. I know what I want to talk about: a short apology for not getting back to him sooner, my majors, the books I read during the summer, my reasons for choosing English as my major, my future goals, and a polite inquiry about his life. The problem is the format and the etiquette. Should I just start with "Dear Mr. XXX" and end with "Sincerely, OOO"? Or are there other things I should take notice? After writing five-paragraph-thesis-statement-and-examples essays for the last three years, it's actually pretty hard to jump out of that box. How organized should the letter be? Is it like a free-write with no format? Do I need a strong ending and a hook for the introduction?

Any help would be appreciated!

PS. He is around 60ish (both of his children graduated from college already, I think) with a bizarre sense to humor. And no, he does not have an e-mail account, not even a computer.

PPS. He likes to read, A LOT, but he's primarily interested in intellectual stuff, not fiction. The only fiction reads are uber oldies like The Scarlet Letter and Shakespeare, if you can call that fiction. My taste runs for fictions. I like oldies too, but just in case, I don't want to bore him with long recounts of story plots...