I don´t think Peter Pan could be older than a teen or the whole purpose of having PP as a villain would be gone… He is the boy who never grew, I know they change a lot of things, but having an adult portraying him would be weird.
This is television, where teenage drama shows always feature 20+ years old actors playing the role of 16+ years old characters. It wouldn’t be a surprise at all, especially when you consider 13 years-old Wendy was played by 19 years-old Freya Tingley and 16 years-old Felix was played by 26 years-old Parker Croft.