My T worked with this theory- and I believe that trauma fractures our personality and we can get stuck at the age when it occurred.

I always used to feel fragmented. The 7 year old part was always there. As we went on another child part emerged. Both of those ages are linked to events for me. I didn't remember the event for the 7 year old part, but actually recalled it following a dream which triggered a memory. The 4 year old part couldn't talk and only cried because at that age I didn't have words. We gave each a name and each one was allowed to talk and with time the 4 year old part found her voice.

T helped me see that even though I had those parts it was still me and a goal for therapy was integration . Close to two years in therapy I've realized that I actually don't feel each part as strongly.

Not specifically related but you might like the book the body keeps the score.