"Be one's age" refers to acting or behaving in a manner that is appropriate for someone of a certain age. Some synonyms for this phrase include: acting maturely, being age-appropriate, behaving one's years, following societal norms, and adopting a responsible attitude. It is important to note that these synonyms are subjective and may vary depending on culture and values. Furthermore, the notion of "being one's age" is a societal construct that may limit individuality and personal growth. Therefore, it is important to balance following age-appropriate behaviors while also allowing for individual expression and creativity.