I'll take any age 36 too old for you, send her along!
Louisa May Alcott (in 1868, paraphrased): "Calculate the age of the bride by taking the groom's age, divide by two, and add seven". Examples:
Boy 16, girl 15
Boy 20, girl 17
Boy 30, girl 22
Boy 40, girl 27
.
.
Boy 70, girl 42