"Old" defined

Tonight we were at the park with a few other families from church. I was pushing my kids on the swing, and Son was telling me about how smart Claire is. Claire is 5 years old which means she is so much wiser that the 4 year old. "She is so smart she will be my teacher some day." I told him that she wouldn't ever be his teacher b/c she isn't old enough. Thinking he would say me I asked, "But do you know who will be your teacher?" "Who?" "I will." "Oh, no Mommy, you're too old to be my teacher." "What!?" "You're going to be really old, and when people get really old, people die." It is nice to know that I'm almost really old!