I'm not a fast quester, but I'm not by any means a slow quester and I've put a good solid ammount of hours into getting to only level 18.
I feel that with a 1x exp rate that the ability to talk in channels like Global should be granted at a lower level then 20. Maybe not too much lower, but 15 would be reasonable or 10.
I just feel that at 1x exp rate when you're doing every single quest, it can take a while to get through the first levels.
This is a valid point, whatever the lowest level you can enter an instance should also be the level you can talk in chat channels, I cant see it being useful at lower levels than that
I would suggest level 10 as the required level to talk in global chat channels. It takes a good few hours to reach 10 usually, being able to talk to people would be nice.