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Sometimes I wonder this. Am I old? Not physically, I mean I am only 21 after all; I'm one of the youngest members of my guild. I'm actually younger than most people I know on WoW, despite the stereotype that Horde/Alliance are 13 year olds (depending on your faction).
But I find myself often being the oldest character in most situations. I know about 6 other players who have been playing the same length (and 2 longer than me) of time on my realm. I'm sure they're are far more than that, but all considering, most of my realm are Burning Crusade Babies (as I like to call them). And now we have an even larger rush of Wrath of the Lich King Babies, and alot of these people are returnee's to WoW after TBC.
I've been playing my Hunter main, Rikaku, for 4 years. She's been the only toon of mine to actually hit the level cap, despite the fact I have over 20 alts of varying classes and levels. I don't consider myself a Hunter guru by any means (but ask me about the Lore of a quest, I dare you!), I'm just your regular Hunter casual who enjoys a good quest and loves mount-loot. But with this large influx of new players, I find myself often quoting things of the past that just go over newer players heads.
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Now, don't get me wrong, I'm not saying there isn't memorable stuff in Wrath of the Lich King. There is! Between fighting as Arthas against Illidan, to the Wrath Gate, to defeating Malygos; there's memorablia in it all. But sometimes, there's fond nostalgia. "Time makes the Heart grow fond", and I think that's true for the old dungeons. With the Achievement system implemented, there are daily Molten Core, Blackwing Lair, Ahn'Qiraji & Zul'Gurub runs, you name it.
So, take it from me, if you haven't ran any of these dungeons before and you're a BC/WotLK Baby, run one of these dungeons. If you're a mount collector, achievement-collector, aspiring Loremaster, or even just a collector of neat looking weapons, there's something for you in the old dungeons; Just gotta dust them off and experience it.