It’s also likely that if Pan is Malcolm, he doesn’t initially have those memories if ever.
But then how does he remember stuff like how Rumple likes his eggs? Because if the de-aged father thing proves true, I’m guessing it spelled the end of their relationship, (with Pan going to NL pretty much immediately after, perhaps actually at the exact same time), so there were no more shared breakfasts after that point. We’ve seen with August that being de-aged takes away your memories, so you’d think that Malcolm being de-aged to the age he was when Rumple was born, (if the teen father thing were true), or even younger, would wipe out any memories that he had of Rumple’s life, like how he likes his eggs.
Also, just on the name thing, unless Malcolm changed his name, he can’t be the same person as Peter Pan. I know it’s been discussed before that Peter and Rumplestiltskin is an odd pair of names if the same people (their parents) named them both. But I could see if is name was originally just Peter, and when he went to NL, he added the Pan on because he got himself a god complex. Why would someone named Malcolm completely rename himself Peter Pan?
PS. Yes, the casting department are freaking geniuses. I swear they have facial recognition software that they run actors’ headshots through.