A man old enough to be a grandfather is wanted for armed robbery in Shenandoah.

Early Saturday afternoon, police said an armed man believed to be in his 60s walked into the Valero store on I-45 near Research Forest Drive and told the clerk he was robbing the place.

Investigators said the clerk didn't believe he was serious at first, but quickly changed her mind when she caught a glimpse of the gun.

The suspect took off in a light-colored Buick four-door sedan with temporary tags, investigators said. He is described as Caucasian, around 6-feet tall, 250 pounds and wearing a white t-shirt with "FBI" written on it.

If you have any information, you are asked to call the Shenandoah Police Department at 281-367-8952.