There are a lot of humans on Earth and so a lot of humans have been exposed to things as children they aren't equipped to understand. How it affects a person depends on the person. If you were aware of it at that age, maybe. If you weren't aware of it and only found out later, maybe not. You might have experimented anyway, lots of people do and lots of people don't. Again, lots of humans around and so lots of different ways of behaving. How much our past experiences affect us depends on our individual personality, and how bad the experience was and how profoundly it was felt at the time. If you were repeatedly and intentionally involved in porn at that age, that's an abnormal childhood. If it happened once accidentally, then maybe it's not. Lots of adults like porn and lots of kids have walked in on their parents. But that doesn't mean everyone understood what they were seeing or that it had any effect on them. So the only important issue for you isn't what's normal, it's whether it's bothering you and interfering with your life. It sounds like it is. Which makes it a mental problem of some kind. If it's bothering you a lot, it might be time to talk to a professional therapist about it and get this resolved and out of your life so you don't obsess over it and make it into something that does bother you enough to interfere with your development.
Do not regret your experiments. They mean no more than that you are open minded, bold, high IQ etc. Drop it. Enjoy