FWIW, I remember almost nothing from before 6. I can remember a few extended memories aged 6, then quite a lot from about 8 onwards. The absolute earliest memory I can dredge up is age 5 but we're talking a mere snatch of an image. I have bizarre time and memory dilation issues in any case so my brain isn't quite representative of the norm!

My father, on the other hand, goes to the other extreme and claims to remember being in his pram in the garden at about 18 months old and not being able to understand the noises being made by other people around him.