Say im lvling my Crusader through Adventure mode and get some rift Keys (possible?) do you have to wait till 70 to use them or can you use them whenever or is this hypothical situation null and void cause you dont get keys to drop until 70 anyway ?
No, Rift Fragments drop independent on your level, and you can use Rift Keys to open Rifts on the level that you are, and do them normally, from what I remember from the RoS beta (when leveling my Crusader).
Pretty sure of that at least, don't quote me on it though, since I'm a half asleep zombie right now =|
They made comments about wanting to change it but they never changed it during the beta. So, AFAIK it should be the same but ya never know. Always helps to be prepared with all da knowledge!
Just making sure you know: You have to complete Act V to unlock Adventure mode. I think you can indeed do Rifts at any level though, there haven't been any blue posts specifically mentioning otherwise.
You only have to complete Act 5 on one character, and you have to do rifts in Adventure mode, other than that no other restrictions exist besides the amount of rift keystones you got.
Pretty sure of that at least, don't quote me on it though, since I'm a half asleep zombie right now =|