Light travels at about 1 foot per nanosecond. You could do an experiment on a six-foot lab bench and measure the time it takes for light to travel the length of the bench and back as 12 nanoseconds. If you were six feet tall, would that have any bearing on your measurement?
Now if your nerves carried signals at the speed of light and your brain could process information really fast, you might have a hard time walking because there would be a 12 nanosecond delay between your eyes and brain telling your foot to avoid that hole in the ground and you seeing your foot reacting. So your huge observer would have similar issues but keep in mind that gravity would collapse any such being into a near-perfect sphere, just like planets are so it's really something that is impossible to happen.