Going over the hill is an idiomatic expression that refers to the process of aging or reaching a point of decline or deterioration. In terms of antonyms, there are various words and phrases that can be used to describe a state of youthfulness, vitality, and growth. These antonyms could include terms like "coming into one's prime," "flourishing," "blossoming," or "reaching the peak of one's powers." Other antonyms might reflect a sense of rejuvenation or renewal, such as "emerging from a slump," "revitalizing," "reinventing oneself," or "rediscovering one's passion." Ultimately, while going over the hill may imply negative connotations, its antonyms can evoke a sense of optimism and opportunity.