I think it was helpful to me to separate sense impressions as a concept from memories. Sense impressions, whether they're visual, auditory, whatever, I think can originate and persist from very young ages. But memories to me imply narrative, and that demands a certain level of cognition and is subject to the over writing influence.

I have a couple of sense impressions from young enough to be in a crib, but able to pull myself up and "stand" but before being really able to walk. But I was also told an anecdote about that experience, so the two together have formed a created memory.

I also have trauma impressions from an experience @ 3 years old that is more concrete, but still not really a memory because there is no narrative attached (never referred to by others, no anecdotal evidence to supply an over write).