When my son was about 3 years old, we were visiting my dad. My dad said to him, "I'm so proud of you. You're quite a youngster."
My son said, "Pappaw, I'm proud of you, too. You're quite an oldster."
Already chuckling, I asked my son, "If you're a youngster, and Pappaw's an oldster, then what am I?"
He quickly replied, "You're a monster."