How much younger do comparators have to be in age discrimination cases?

In discrimination cases, plaintiffs often rely on comparators. If the plaintiff was treated worse than a similarly situated co-worker who differs from the plaintiff with regard to a protected characteristic, then that creates an inference of discrimination. 

Not official use.

Ordinarily, there's not much dispute about whether the comparator is a different race, or sex, or national origin. But, age discrimination poses a unique problem. No joke, I once had a plaintiff try to use someone 8 days younger than him. Was that really evidence that the employer discriminated based on age? Of course not! So, how much younger does the comparator have to be before the Court will infer age discrimination?

Here in the Third Circuit, including Pennsylvania, that cut-off appears to be in the 5-7 year range. See, Narin v. Lower Merion School District, 206 F.3d 323, 333 n.9 (3d Cir. 2000) (7-year age difference between 56-year-old plaintiff and 49-year-old comparator was insufficient to “permit an inference of discrimination”); Gutknecht v. SmithKline Beecham Clinical Lab., 950 F. Supp. 667, 672 (E.D. Pa. 1996) ("Although no uniform rule exists, it is generally accepted that when the difference in age between the fired employee and his or her replacement is fewer than five or six years, the replacement is not considered sufficiently younger, and thus no prima facie case is made").