Life as an improvisational art, at every age. This idea animates the wise linguist and anthropologist Mary Catherine Bateson, whose book “Composing a Life” has touched many. Since her childhood as the daughter of the iconic anthropologists Margaret Mead and Gregory Bateson, she’s had an ability to move through the world as both an original observer and a joyful participant. Now in her 70s, she’s pondering — and living — what she calls the age of “active wisdom.” She sees longer life spans creating a new developmental stage for our species.