If you believe my mum, I started to draw before I started to walk or talk. Honestly, I could believe this (even though my mum has a tendency to exaggerate stories), because she kept a lot of my very old drawings, and my right thumb is a few millimetres shorter than my left as if the shape was affected by holding a pencil or something a lot from an early age!
The story goes, that when I was taken to the clinic for my assessment when I was two years old, the nurse asked me to draw a person (like they did for every child that age at the time), and I refused to draw a person and drew Benjamin Bunny in a Tamoshanta hat, like from Beatrix Potter's "the Tale of Benjamin Bunny". The nurse, in this little Northern rural town was a bit stunned by this. 
Apparently, as a toddler, I used to ambush any adult who visited the house with paper, a crayon and the command to "DRAW THOMAS", and if they couldn't draw a satisfactory picture of Thomas the Tank Engine, I would scream.
The only person who ever drew a good enough picture of Thomas to leave me satisfied was one of my cousins. All the drawings I did at that age are of these things that look like spiders or a smiling sun; a smiley face in a circle with lots of lines coming off. I'm pretty sure I was trying to draw Thomas than Tank Engine and frustrated by my inability to do it because I was a baby.