I've never been diagnosed and stopped by because of a friend (I'm personally interested because of some problems I had while living overseas, though they were never diagnosed as PTSD, and I didn't ever show all of the symptoms). Anyway, I don't know who's childhood is normal, and I couldn't tell you what is normal for you or anyone else--in fact, I suspect that it varies a bit by individual.
My earliest memory is when I was 2 and a half, I can still picture the moment from first person (which is pretty rare for me and, as far as I can tell, for most people. My stress in this moment and my stress memories from my miserable moments overseas are both in the first person). I know I was 2 and a half because I was still in a crib until just before my 3rd birthday. My brother and sister and I had stolen the scissors in the den (under the nose of our babysitter) and we had cut our hair on the living room carpet, discovered to the rage of my father when they walked in the door from their night out.
Several of my memories as a child were of moments that were filled with emotion--very exciting, very afraid, in a lot of pain, surprised or experiencing something novel (a blizzard when I was 4). Usually when I'm shown a picture, I can remember the event or similar events. Sometimes when my parents or sister/brother remind me of an event, I can remember and other times I just can't. Usually when someone asks me to remember "typical" events, I can recall something--a time I was punished, a time I did something fun, a favorite toy, favorite activities. However some things that I used to be anxious about or feel emotionally about I don't remember--I was often afraid of talking to people for the first time but all the memories I can remember are from when I was 5th grade or older and had a paper route (and frequently had to speak to people I didn't know). I'm sure there were earlier moment, but I couldn't tell you what they were. But other things which used to regularly stress me out I remember very clearly, and I think that I remember many or even most of them. In fact I felt like I was supposed to remember them, so I did, as if I were on the watch for them.
I remember being fascinated by the idea "repressed memories" when I was a kid and first heard about them, and I struggled to remember things that I couldn't remember. But the first time I remember "blanks" in my memory was after I returned from overseas. While I was there it was as if my eyes/memory was glued open, but when I returned home I couldn't pay attention, didn't care to, couldn't remember meetings I had been in, etc. I remember watching a movie on the plan home, but it took me 4 years to remember where I had see it--I couldn't account for where because there was no "contextual" information in my memory of it; I could only remember that I had for certain seen it and knew what was coming next.
If you had a generally unpleasant childhood, it may be that you just don't want to remember even if you could, or it could be that you don't have much to remember. My parents weren't very fun to be around when I was young, and I don't have very many "happy" moments with them where I 1) wanted bond or do something special with them or 2) enjoyed being with them. Someone told me once about waiting at the end of the block for their dad to come home from work and I can honestly say that I don't remember ever doing that because I never thought my mom or dad returning from work was something to celebrate or look forward to. So sometimes I know I don't have any memories of something--or at least haven't stored it in a file labeled under that category of memory. I'm sure if I thought hard about it I could remember a time before the age of 8 when they came home from work and I was around to notice.
I'm pretty sure that I have an above average memory and I tend to remember images pretty well. I know people who think/process information more abstractly and they don't tend to remember as much, it seems. Maybe it would be helpful to ask yourself if you really want to remember any of these details. Or maybe ask yourself what kinds of gaps you have. Are they selective--only certain types of activities? only certain times of the day (night, for example?) only around certain people that you are sure you must logically have interacted with a lot? Or is it just that you can't really remember much at all before age 8? Are all your early memories fuzzy? Also, in my experience, gone is different from fuzzy. There are things I don't remember from childhood, but I feel like I don't care much (though I was admittedly a bit dissociative as a kid). But the memories I couldn't seem to get back as an adult felt...conspicuously absent. There should have been something there where there was nothing. There was space in my head for it, there were logic gaps--memories of the airport the day I left to come back and then suddenly I was standing at the trunk of a friend's far watching her put my suitcase in her trunk and she was asking me if I would go eat dinner at my boss's boss's house. I can't answer what it's like for those with trauma as a child who have memory issues, but a comparison might be helpful