I have a 60-year-old sister named Joanne. She lives with an intellectual disability. It used to annoy me when people asked me what Jo’s “mental age” was. It’s not as simple as saying she’s like a six-year-old or an eight-year-old. She lives in a group home near me, catches public transport, works at a social firm (what used to be called a “sheltered workshop”), uses a cell phone and mucks around on the internet, all things adults do. But she also likes playing with dolls, coloring books, and she has a vivid fantasy life.