I started copying BASIC code out of books and modifying lines when I was 4 on the Commodore64. I pretty much learnt to program in BASIC at the same time that I was learning to read and write. The C64 had an awesome intro to BASIC book (I still have it!) and Osbourne used to publish some good stuff to for BASIC-enabled "microcomputers" like the C64 and VIC20.
Started writing my own stuff from scratch just before I was 5. I still remember a dodgy car game I tried to make named Cataza - the car was made from ASCII (or ANSI?) art and you basically had to press the correct key at the right moment to shoot stuff. It was just one huge linear program that would draw a frame, play a note of music, see if you press the right key within half a second or so, then draw the next frame, play note, etc..
Got an Amiga 500 when I was about 8 or 9, and things really took off from there - especially a couple of years later when AMOS came out. Is it a sad thing that my 2 month old son has the middle name "Amos" because of the programming language?
Heh, after 25 years of programming games in many languages, I still think some of the stuff I did before I was 10 was my most creative and impressive work!