Great question MsFriz and one close to my heart since I come from an art background. The 'normal' age of drawing simple figures that are recognizable is 6 to 7 yrs old. This is drawing figures with facial features.
My daughter was no longer scribbling before she was 10 mths old. She was able to control her markings and draw letters such as O, M, H, W by this time. She is now soon to be 2 1/2 and draws complicated creatures. Sometimes they are animals such as a baby bird in a nest which I took a picture of before she erased her doodle pro.(lucky me for having my camera on me at the time.) Sometimes they are strange creatures with facial features. But all have volume and specific features.
I was able to draw complicated figures before I could walk, so around 13 mths and definitely showed signs of artistic talents at an early age. The best thing you can do for your son is to let him explore his abilities and have plenty of art supplies around for him. Every Christmas I would discover a big pile of art supplies under the tree which was definitely a joy.
