I read that as age-difference which is also false. It is genetic "difference", e.g. one paragraph from the abstract

"In each case, increased homozygosity was associated with decreased trait value, equivalent to the offspring of first cousins being 1.2 cm shorter and having 10 months’ less education"

I read this as “the greater the age gap” at first.

> not "further apart" in distance

And also not further apart in time :p