WoW isn't just for kids or spotty faced teens. People of all ages play and enjoy it for various reasons. If I am not mistaken If the OP is the person I think he is even people in their 50s enjoy the game. I've tried it a few times myself and can see the appeal.
The game is simply: you take on a character in an online world filled with other people's characters and some game-generated characters. You roam through the virtual realm interacting with characters, going on quests and forging relationships. You earn points for quests and various activities which elevates your ranking in the game giving you different advantages as you advance through the ranks.
As far as cost goes, you can play for free as a trial then its a small monthly subscription you can pay month by month using scratch cards bought at game shops or you can pay yearly via credit card. If you compare WoW to other games it's actually one of the most cost effective. If you look at new Xbox games they cost £40+ per game along with cost of console, controllers, batteries. etc/ WoW is played on your computer with no special devices or software to purchase.
I watch my nephew play it and its a very social game. You make friends with people around the world and form 'guilds' which are just groups of people that work together to accomplish more complicated quests that require teamwork. Using voice communication works to the guilds advantage as during battle sequences you can shout at your fellow guild members to run or duck or attack a new foe. Using skype for this removes you from the game communication channels which as flaws.
If you like castles, dragons, knights, treasure hunts and making new friends I recommend you give WoW a try.