>>29482628There were interviews saying 16, and interviews saying 14. I haven't been able to find any of them, and the links on bulbapedo are down.
If we look to the Manga adaptations, Hilda/Hilbert are portrayed as 16, but Rosa/Nate are 14. So it's possible that they were intended to be 14, but were at earlier points in time considered 16, with the manga already sticking to that.
14-16 just seems like an accurate ballpark, so headcanon whichever you see fit.
>>29482506As NPC/Rival characters, they are their own characters. Lucas and May for example. But as the player characters, they are blank slates. It's why Red doesn't talk, and why Ethan/Brendan in Generations were kept as vague as possible, outside of Brendan picking Sceptile.
>>29482557Don't be a fool. While Red is the only previous character to physically show up in other games, nearly all other protagonists have been referenced at some point. Cynthia in B/W references the Gen 4 Protagonist and how they calmed Giratina, for example.