The great thing I find with the game, is what worries you, which I'm about to point out it not necessarily a problem. - konfoozed? - Let me explain:
The Level Divide is NOT a deal breaker @ all - A level 10 guy can easily run around and do quests with a Level 20 guy.
The reason for this is quite simple.
Every Quest has a level, each region in the greater area (call it the starter area) that we are in has level 1-20 quests. The quests are open to EVERYONE, unless of course you’ve already completed them

You get the SAME rewards no matter what level you are; eg: Level 10 Guardian, Level 20 Hunter complete quest X together as a team (ie. Both have accepted the quest) and return to the quest giver to complete the quest. Both have to individually compelte the quest and both get 120XP and a a Hat of Armour +53. There are no added bonus’s or subtractions for either player. The only caveat was that it was perhaps a level 10 quest (doesn’t HAVE to be, but in the example it was), but as you can see there is no meaningful reason why they couldn’t do it together, they both get the same rewards.
It then boils down to what level of questing you can/should be doing.
Last night our little questing party decided to do a level 20 instance quest and after 30 minutes of battling it out, realised that we were thoroughly unprepared for it and got our asses handed to us.
I personally lost two items of armour (one being my pants) from the whole thing.
So now, after that little romp, I need to go back and do some level 12-15 quests in search of quests that reward me with pants

Anyway, you get the idea.
The bottom line of it all is to all just meet up, go grab quests TOGETHER and go do them.
There isn’t really any Level divide as such – even if it feels like it at first.