We are 5, former 8 from the 70s.
There's 5 current members, with three additional past members (totalling 8) and they're from the 70s.
One of us has the voice
Steven Tyler is the singer of the group and also a judge on American Idol (which is not quite The Voice).
One of us has the Katy
Joe Perry shares a last name with Katy Perry (since she changed her name from Katy Hudson), though they are not related.
The first went from the World to the Country
They are a world-famous rock band and now Steven Tyler has released some country songs (though not with Aerosmith).
We ran with McDaniels
Run DMC (with Darryl McDaniels as a member) rerecorded Walk This Way with Aerosmith.
And we've been heroes
They have a Guitar Hero dedicated to them.
Some say we're crazy
For playing with the toys in the attic
But there's not a sweeter emotion
than lovin' in an elevator
Crazy, Toys in the Attic, Sweet Emotion, and Love in an Elevator are all Aerosmith songs.