The "never date anyone under half your age plus seven" rule is a rule of thumb sometimes used to prejudge whether an age difference is socially acceptable.
Although the origin of the rule is unclear, it is sometimes considered to have French origin.
There is no scientific evidence to support the rule.
In the earlier sources the rule had a different interpretation than in contemporary culture, as it was understood as a formula to calculate suitable age for the bride, instead of a lower limit for the suitable age.
Max O'Rell's Her Royal Highness Woman from 1901 gives the rule in the format "A man should marry a woman half his age, plus seven."
Similar interpretation is also present in the 1951 play The Moon Is Blue by F. Hugh Herbert.
The half-your-age-plus seven rule also appears in John Fox, Jr.'s The Little Shepherd of Kingdom Come in 1903, in American newspapers in 1931, attributed to Maurice Chevalier, and in The Autobiography of Malcolm X.
In modern times this rule has been criticised as being more accurate for men than women, and for allowing a greater maximum age for a woman's partner later in her life than is actually socially acceptable.