When dealing with human beings, no statistical statement will ever be 100% accurate. If you want to get technical, (and none of my references were) you would have to specify standard deviations and what the population sampled was. (If you saw 10 baby elephants, you would conclude that all elephants were 4 foot tall.) But, the idea is to get a general (not 100%) idea of what elephants look like. Regarding four-year-olds, I think my depiction is quite accurate. I don't think you will find too many mothers who have 4 year old little girls would disagree. Both my kids, at four years old, approximated it all.

As for adult memory reaching back as far as you describe, I have heard of people doing that. Just not me. My earliest is from first grade.

By the way, my title to this post is a joke. Let me know if you want me to stop being silly with replies to you. (All in good fun.)