A Brooklyn grandmother was robbed at knifepoint during a home invasion Wednesday – as she became the latest victim in a disturbing uptick in attacks against the elderly, authorities said.

The 81-year-old Sheepshead Bay resident heard a knock at the door around 12:15 a.m., and opened it to find a pocket knife-wielding man skulking outside, cops said.

“She heard the doorbell ring; she came out, and she was saying ‘Who is it, who are you,’ and the person was saying ‘It’s me, it’s me,'” the woman’s 54-year-old son told The Post.

“She assumed it was me.”

The crook pushed the woman into a back bedroom, where he demanded her purse and money.

“He said, ‘Where’s the money, where’s the money?'” the son said, quoting the robber.

“He said, ‘You gotta have money. Take me to where your pocketbook’s at.'”

The crook then explained that he needed the cash and warned her not to tell anyone.

He fled with the bag, which contained her cellphone and around $300, police said. The victim was not injured.

The suspect is described as a black man who was last seen wearing a checkered scarf and all black clothing.

“She’s shaken up and scared. She doesn’t want to talk,” the son said, noting that his mom has lived in the neighborhood nearly 50 years.

“I feel safe, but to prey on the elderly? What’s the world coming too?”

The incident continues the disturbing trend of attacks on the elderly. More than 300 Big Apple seniors have been mugged so far this year, according to police officials.

Robberies against senior citizens are up 6.5 percent this year, with 371 victims so far this year as of Sunday. There were 348 during the same period last year.

Assaults against the elderly have climbed 16 percent this year, with 1004 victims, according to NYPD statistics. By comparison, 863, fell prey in 2015.