There is no definitive answer to this question as it varies depending on the couple's individual circumstances. However, research has suggested that divorces are more likely to occur during certain life stages. For example, divorce rates are highest during the first few years of marriage and when couples reach middle age (around 45-50 years old). This may be due to increased financial and familial obligations during these periods, which can put a strain on relationships. Additionally, couples who have been married for a long time may be more likely to experience boredom or resentment, which can also lead to divorce. Ultimately, there is no easy answer as to what age is hardest for divorce - it depends on the couple in question and their unique situation.