I've had a best friend ever since I can remember. She's three years older than me, lives two houses over, and I've known her since before I could walk - in other words, for more than twenty years.
When we were little, my parents - being the defeatists they sometimes are - used to warn me that people grew apart; that some day my best friend would forget about me and have other things to think about. They wanted to prepare me for the day when she, being three years older, would get bored with me and move on with her life. I defiantly told them that wouldn't happen. And lo, I was right. She never outgrew me, and even when I sometimes think I've outgrown her, she shows up and proves me wrong by saying something absolutely amazing.
Sometimes I remind my parents that she and I are still the closest of friends; not to rub it in their faces, but just to gleefully remind us all that true friendships aren't predictable at all, save for the fact that they're sure to last. She's the one person in the world who just gets me, without my having to explain it at all.
Now if you'll excuse me, she and I are going to eat junk food and discuss yesterday's rather successful party :)