things a new player might have missed

[Enkidoh]

Well, to be fair the way the game is designed because sidequests reward experience there is an expectation that the player will be actively seeking out quests from npcs and thus keeping themselves up to date with questing by going back to areas they've already been and seeing if there are any quests available. But it is easy to get sidetracked and forget about them though.

Either way, this is a list of all known level-locked content and where and what level to unlock it:

A Realm Reborn level locked content guide
Heavensward level locked content guide