Difference in age was one of the reasons for the couple's incompatibility.
不釣り合いの夫婦
an ill-matched couple
(身分が)不釣り合いの結婚
an unequal marriage
男女間の給与の不釣り合いを正す
correct the imbalance between the salaries paid men and women
あなたの暮らしぶりは収入に不釣り合いだ
Your way of life is not appropriate for someone of your income./〔収入の割に質素な生活〕Your life-style is not commensurate with your income./〔収入以上の生活〕You're living above your income.