To understand why we recommend beginning your child's math lessons before the age of two and a half, it is important to understand the concept of perceiving quantity - also known as "subitizing."
At birth, the right hemisphere of the brain is dominant over the left. This makes sense, as many autonomic functions - critical for the baby's survival - are governed by the right side of the brain. The left side of the brain, which governs rational thought, comes online later - which would explain why it is next to impossible to reason with a very young child!
In most people, the brain shifts dominancy from right to left by around three and a half years of age. The process is a gradual one. It should be stressed that almost everything we do involves both hemispheres of the brain working together. However, the degree to which one hemisphere dominates over the other does affect how we perceive the world - and as a result, our ability to learn.
The right hemisphere is markedly better at absorbing pictures than the left. If you are extremely right-brained, as certain savants are, you might be able to perform the seemingly impossibly by, say, producing an entirely accurate aerial map of a landscape you have flown over just once - right down to the exact number of windows on the farthest visible building.