This is kind of a general "has this ever happened to you?" kind of question.
I started playing WoW back in February with some friends, and we planned on leveling together all the time. By the time our characters hit the 40s, I had pulled ahead by a few levels, and the gap just kept widening because my friends suddenly decided they were tired of WoW and didn't want to play much. (Much = at all.) I wasn't tired of playing and liked soloing, so I just kept going. (Also, I was not in a guild.)
I was lvl 56 in Winterspring and a random guy was LFG to find that bear (Ursius or something like that?) so I was like, hey, I need that, and grouped with him.
Almost 10 levels later, we've duoed all of Hellfire together, got kind of split up in Zangarmarsh (but we both helped each other catch up, so we've done most of the quests there twice) and are moving on to Terrokar/Nagrand. We've also started playing alts together. (And... still not in the same guild, haha.)
Another little tidbit - I'm 22. My leveling partner is... 14. Um, lol? I could tell he was young but when I found out how young I admit to being a little weirded out, but my brother's the same age so I'm not totally out of my element talking to him. He's a cute kid and I can get excited about dumb stuff with him and he won't think I'm immature. ;)
Anyone else have any unlikely leveling partner experiences?