The phrase "the wrong side of forty" is often used to describe someone who has reached middle age. However, there are several synonyms that can be used to express the same idea. Some alternatives include "past their prime," "middle-aged," "over the hill," and "past middle age." These terms may have different connotations and levels of formality, so it's important to choose the right word for the context. While some might consider "the wrong side of forty" to be negative, these synonyms can help to soften the blow and convey the concept of maturity and experience instead.