She’s in it for the long run!

A tough-as-nails 80-year-old New Jersey grandmother became the oldest woman ever to finish the grueling Ironman World Championship over the weekend — and now she says the key to staying fit in old age is to “keep moving.”

“I’m never close to giving up,” Natalie Grabow, of Mountain Lakes, told The Post Thursday. “I love the feeling of working hard and accomplishing a goal.”

Grabow has competed in 10 other Iron Man races on the island. Getty Images for IRONMAN

Grabow pushed through a minor hamstring injury, rough waves and intense humidity to run 26.2 miles, bike 112 miles and swim 2.4 miles in the open ocean on Saturday during the race in Kailua-Kona, Hawaii.

The mother of four and grandma of two completed the notoriously tough triathlon in 16 hours,

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