As a Medium, I have had many people ask me when I started 'seeing' or 'knowing' things. I always have. I don't know why I did and others don't. (I could not have explained it to other people in words at the time).
For as far back as I can remember, even as a small child, there was a woman (a spirit) who used to stand in the right hand corner of my bedroom and talk into my head. (she was always in the right hand corner no matter what way my bedroom was arranged). I was deathly afraid of the dark and she lit up my room for me and told me/made me feel like everything was always going to be all right. (my bedroom door was open and the hall light was on but that wasn't enough)! She told me that she would stay there until I fell asleep and she was there every night for years. I would go to sleep and have the most wonderful (almost always) dreams in color that I was flying and visiting people and places. I could see her almost as solid as a 'real' person and I thought she was my Aunt. (one of the ones from the other side of the family that I don't look like. You know, the tall, thin, blond, pretty ones! Ha! Ha! She DID look like my cousins)! I felt safe with her there! I knew not to tell anyone about her or the other things that I was seeing! (I don't know why I knew but I did).
(When I found my spiritual teacher and asked her about this woman, she said that she was my Aunt (further back) and that she took me on astral travels (flying dreams to other places).