She's only 13, but this British girl has suffered a lifetime of insults — thanks to a rare genetic disease that makes her look decades older than she actually is.

"I see saggy skin... It's like I'm a young girl trapped in an old woman's body," said Zara Hartshorn, who has suffered since birth from lipodystrophy — an affliction that causes the layer of fatty tissues under the surface of the skin to disappear.

Zara, a bright teen with an infectious laugh, told The Post she is often tormented by bullies at school.

"People call me 'granny' and 'monkey,' " she said. "Sometimes I'll just go into the toilet and cry."

But the teen, from Yorkshire, doesn't take it all lying down. "Sometimes I sass them back and then I run," she said.

Her mother, Tracey Pollard, 41, knows exactly how Zara, the youngest of her six children, feels. Tracey has spent a lifetime battling lipodystrophy, which also affects two of her other children.

Dr. Abhimanyu Garg, a professor of internal medicine at the University of Texas, says it has numerous causes.

Only about 2,000 people around the world have the hereditary syndrome. But lipodystrophy can also be contracted "as a side effect of drug therapy or associated with other immune disorders," he said.

There is no cure, but some victims can undergo appearance-improving procedures like cosmetic surgery.