Here is my tallest sunflower. My son is 6'2", taller with his shoes on, and it towers above him. We haven't measured but estimate it to be around 12 feet tall. It has a bunch of little flowers that will open soon.
I'm not sure what type of sunflower this is and if it was supposed to get this tall. I don't know how I got my 16 year old to grow that tall either. Don't tell anyone but he is taller than his dad.