The antonyms for the phrase "reaching adulthood" refer to a variety of stages that come before and after this significant milestone. Childhood, adolescence, immaturity, naivety, and infancy are some antonyms that depict earlier phases of life, where we are still developing and gaining experience. On the other hand, middle age, elderliness, old age, and senescence are words that represent the later stages of life, where we begin to lose some physical and mental capabilities. The antonyms for "reaching adulthood" suggest that life is a continuous journey that involves various stages of growth, development, and decline. Each stage brings with it unique experiences, challenges, and opportunities.