He doesn't remember how he looked like when he was a kid?

It was a bit convenient to the story that the kid's identity was somehow disguised from his 40 year-old self. I don't think that there is any way that the kid playing his 8 year-old character would have grown up to look like Bruce Willis.

Would you believe right away that your younger self was standing right there in front of you?
Then again his older self has memories of the events. How come he didn't remember the meeting?

He does remember but he tries his absolute best to block out that moment in his life. He was very insecure with his image as he was bullied, mom died, and felt defeated by his father.