I am extremely good at memorizing things and do it for fun.
High school was a breeze because they didn't teach learning - you just had to memorize the answers and regurgitate them onto the test. In a history class, we had to read a chapter then deliver a 5-minute oral presentation on the chapter. At first, the teacher said we could have one 3x5 card with some notes, but when he saw how much the kids were cramming onto their cards, he said "You can have 5 words only". So, just to blow them out of the water, I memorized every single name, fact, number, and date in that chapter. I went first and recited everything. I saw one classmate just drop her jaw while I was reciting this. I was (and - sorry - still am) a bit of a show-off.
College was an eye-opener because I actually had to have an understanding of the material, not just memorize things.
I memorize stuff all the time, just for fun. I have hundreds of poems memorized just because I like them and want to have them with me wherever I go (I think reciting them is a soothing activity for me). I memorize scriptures, song lyrics, quotes, etc. - anything that I find interesting.
I've tried tracing it back to see when it started and I don't think it ever started - I think it's been my entire life. I memorized the words to The End of the World as We Know It, by R.E.M. this spring. I memorized Jabberwocky in college. I memorized the Greek alphabet in high school. I memorized The Cremation of Sam McGhee in 5th grade because we were all required to memorize a poem so I decided to do the longest one on the list. I memorized a song about the chicken and the egg in third grade. I saw Red Skelton perform live once at around age 10 and he started reciting a funny poem - I immediately went into "memorization mode" so I could have that poem, too. I memorized the names of all the numbers up to Decillion in first grade. All of this wasn't for any other reason than, "I like this. I'm keeping it."
A friend at work has commented that he's never met anyone else that enjoys memorizing things as much as I do.