The Wall was erected sometime after the second war, so you'd probably be a bit younger then that based on the above timeline, but not by much.

I recently created a worgen who was born after the wall because I wanted to make someone who hadn't even seen a dwarf or orc. I realized pretty quickly that might make him way too young, so I got around it by fudging the numbers and saying he was 2 years old or so when the gate went up, and he only has some extremely hazy memories of greenskin monsters. I don't know if that's what you're getting at, but remember that if you're a little creative you can make the kind of character you want, if not the way you want it. :)

I have actually been doing some extensive research to figure that out and the Know Your Lore: Worgens, and the all the worlds a stage: Playing a worgen articles both were very helpful in determining that yes, if you were born after the wall was erected you are about 20 years, give or take one to two. You have never seen night elves until they show up in Gilneas, you have never seen Orcs or Trolls or Taurens or goblins or Draenei. You have seen humans, and that's it. You MAY have seen a forsaken if you stood up on the ramparts of the wall and looks over if any forsaken were meddling about on the other side.

What I am trying to find out, now, is how long has it been since the worgen invaded gilneas to when they reentered the alliance? I understand it's been about 10 years, so that'd make most characters born after the wall was raised around 10 years old when they were turned into worgen. They certainly weren't born that way, unless they are only around 10 themselves. Young children at the time, so if your character was, say, 4 or 5 when the worgen invaded, making you about 15 years old, likely you wouldn't have even survived the attack. Who's to say, though?

Anyone else have any ideas on that? I'm trying to come up with the age of my worgen, but I'm not sure how old she is, based on when the attack initially occurred. If it was very recent, then it doesn't matter, but it does change her story a bit. She's not created, yet, so I can still easily manipulate the character and change her class or anything based on that.