I've played this game for years and the best thing about it is you will never finish it. It is constently updated with new content, new quests, new stories. In the past, before I joined, there was a big story with some fire war, quite recently there was another big story line with a war against "the devourer" (Which would take too much time to get into) the characters are easy to relate to and get attached to. It's easy to get into and not much skill needed till much later on. You can play forever as a free player but when you upgrade your account with a 1 time payment, that compared to subscription fees of games like World of Warcraft is barely noticable, the game truly opens up. As I said, you don't need much skill to play it so any age can play, but it's so much fun that it dosen't have a age limit. I'm 20 and I still play, and when I was in college, it was the faveourite game of my IT class (between the ages of 16-18).
And if you get boted of AdventureQuest, it has many other games set in the same world you could fall for, like Dragonfable, a prequel to AdventureQuest, or Mechquest, a kind of prequel or sequel to adventurequest. (all 3 with different gameplay styles but still turn based) and quite recently, AQWorlds, a kind of MMORPG, or Warpforce, set at the same time as Adventurequest, just in space. This is a great game for kids of any age, and adults too.