The judge overseeing US President Donald Trump’s impeachment trial has questioned whether the phrase “OK, Boomer” counts as age discrimination.

The phrase made its first appearance in America’s highest court on Wednesday, invoked by baby boomer, chief justice John Roberts.

The Supreme Court justices were hearing a case concerning the standard a federal employee must meet to show their employer engaged in unlawful age discrimination against them.

“The hiring person, who’s younger, says, ‘OK, Boomer’, once, to the applicant,” Mr Roberts said, as he conjured a hypothetical exchange to try to figure out when an older federal employee might be able to win a lawsuit under the Age Discrimination in Employment Act.

According to databases of high court arguments, this is the first time the phrase has been used in the Supreme Court.

“OK, Boomer” has been used by younger people to criticise the less flexible, tolerant and tech-savvy ways of the baby boomer generation.

The justices were considering the case of a veterans affairs department employee who was in her early 50s when she sued for age discrimination after being denied promotions and training opportunities.

In addition to Mr Roberts’ boomer reference, 81-year-old justice Stephen Breyer talked about a made-up supervisor who was considering candidates for promotion.

“I certainly don’t want people who are over the age of 82,” Mr Breyer said, prompting laughter in the courtroom and on the bench.

The nine justices range in age from 52-year-old Neil Gorsuch to 86-year-old Ruth Bader Ginsburg.