Around 10 years old. I used to steal my Grandfathers Playboy magazines that were hidden in a chest in his bedroom. He had STACKS of those magazines! I would take a few home every now and then and after looking through them, I would sell them to the kids in my neighborhood that were getting an allowance from their parents.
That is, until I got BUSTED by my Mother! She made me take back the magazines that I still had....and she made me apoligize to him! I remember asking her...."Why can't I just put the magazines back and not say anything about it"? That was a little embarrasing having to tell my Grandfather that I did that.
But he was totally cool and never got upset about it.
As far as hardcore porn, around 12 years old. Mostly German hardcore since that's where I lived at the time.