I had the same situation. I was the oldest child my father had with my mom although I have siblings that are older that I didn’t grow up with. I’m the only child of my step-father (they had no natural children) so I grew up as an old child and that is what I went with.
I had the same situation. I was the oldest child my father had with my mom although I have siblings that are older that I didn’t grow up with. I’m the only child of my step-father (they had no natural children) so I grew up as an old child and that is what I went with.