I know what you mean, For alliance, go to Ashenvale.
in southern ashenvale theres this spot that lets horde in threw the barrens, and alot of 19-24 alliance camp around and kill horde there, and ive seen horde 19 twinks vs ally 19 twinks go down.
Also STV, for horde, this is basically like the ashenvale equivalent sort of but the enemys are a little higher level, 1v1s shouldnt be a problem and there is always 19s lurking around due to the arena chest, and fishing stuff.