But the flood of real memories doesn't start until nursery school, which was right around 3-4.
On a related note, there's a different type of memory that started to form later and that I can pinpoint to a VERY specific age...I refer to it as "cultural awareness/memory". I.e. movies, songs on the radio, etc. I was born in '78 and my earliest memories of that sort of stuff is all '85 (i.e. 7 years old). And what a year! Ghostbusters, Back to the Future, "We Built This City", "Born in the USA", etc.
I can barely remember any movies/songs from before then...maybe some in 84, but 83 is a basically non-existent to me. So maybe this is the sort of thing they mean when they're referring to "adult memories" ?
Aaaaand now I feel old.
It's theorized that the amygdala has a "gating" function for memory - we tend to recall memories more easily when they're highly emotional (especially anxiety, fear, trauma). I had a cognitive science professor who brought this up and asked people in the class what their earliest memories were - many of them were scary/anxious events (mine was moving out of an apartment and into a house).
I have many very vivid memories from under the age of 5; playing hide and seek, playing with lego, playing outside and being around family members on our family farm, I even remember big family meals from when I was around 4.
I honestly thought this was normal until about 10 minutes ago.
I have some "memories" that have definitely been created by looking at pictures later. I actually remember one particular case where it was a photo of me as an infant in my mother's arms and I told my siblings that I remembered that and that I was sucking on a biscuit (which you couldn't see on that photo). It turned out that there was another photo of the same time where you could see that I was indeed sucking on a biscuit. That "memory" had been created.
However I do have plenty of memories from childhood that were not created later by other means. The earliest being for sure around age 3, when I had eye surgery. I remember a few things very clearly of that period. (because it was different and somewhat traumatic for a 3yo) For the most part these were not reactivated later by pictures or recounted as stories. (because people around probably didn't even remember them themselves for being insignificant to them)
E.g. I remember being pushed by a girl behind me in line in kindergarten, my glasses fell on the ground and one lens popped out and I blamed her for it. I was likely around 4 or 5.
I have recently started therapy and we're doing what's called "lifespan integration" (http://www.lifespanintegration.com/) where we go through life events year after a year and where I try to picture each particular moment to feel like I'm there. One interesting effect is that more memories besides the initial ones written down have come back over time or some come back with more details. I would think that or other techniques (e.g. hypnosis) could help you remember more things.
It probably helps that a lot of these older memories are associated (in my mind) with the previous house, so when I remember a couple of memories from that house, it causes me to start thinking about other memories associated with that house. Just accessing these memories makes them more likely to stick around (but also increases the chance of distortion, as we rewrite the memories that we access).