The last time I looked younger than I was, I was probably about 16. After that, I almost always looked older than I was, which was convenient, because I was often the youngest person in a group--when I started teaching, I was actually younger than many of my students, and I didn't want them to know my age. I didn't really notice how I old I was starting to look until I was about 75, but at that point what did it matter?