What’s the best age gap in a relationship?

We examine the evidence, from divorce rates to life expectancy

When a friend opts to date someone who is old enough to be their parent, a common response is to see if the decision passes the “half their age plus seven” test. The rule, whose origins remain mysterious, has been passed down through generations as a way of justifying or, more commonly, pouring scorn on other people’s couplings. It’s fine for a 22-year-old to go out with an 18-year-old. It’s not OK for a 38-year-old to go out with a 23-year-old, however a 26-year-old would be fair game. The older you get, the wider the permissible age gap: a 50-year-old can venture as old as 86.

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