Ive seen it in Asians, jars, and silvers that are close to 30" i don't know if its normal or not though, but just about every large aro ive seen has a lateral line like that.
i have 2 silvers around 34 inches. both of them have it. and there only 3 years old. i think urs is older by couple years from what i read from other threads. i think its normal..