I have just had to wank myself off three times in rapid succession to ease my frustration after having my 15yo granddaughter with me for a couple of hours while her parents were busy. She is blonde and slim with nice legs, she does a lot of sport at school. She arrived in the tightest and shortest of black minidresses, and every where I looked she was displaying her white cotton knickers, sitting at the table her dress was too short to hide the white triangle of her panties. Tucked up on the settee I could see right up between her legs. And bending or crouching to attend to the dog I could view her knickers for extended periods. I was getting so worked up that I was heartily glad when her parents arrived back to pick her up. It took me buckets of willpower to avoid messing my pants with cum, as I am prone to do. So glad now that I am back on my own and can wank myself back to some kind of equilibrium.