What a drag it is getting old  — especially for JEN, 44. So guess WHO she hates?

JENNIFER ANISTON is NOT making friends with today’s young actresses. Jen says they’re ruining Hollywood’s sexy image by dressing like frumpy grandmothers.

The 20-somethings should shape up and start showing off their shapes, says the 44-year-old “We’re the Millers” star.

“It pains me to see young beauties like Jennifer Lawrence, Scarlett Johansson, Keira Knightley or Emma Stone dress frumpy or in a long gown that looks like their grandmother’s curtains,” Jen told a pal.

“Older, piled-high hairstyles and caked-on makeup also gall me.

“This is the time they should go with as little makeup as possible and dress as edgy and young as they possibly can.”

In a recent interview, Jen didn’t name names, but sources say she was clearly addressing young starlets Lawrence, 23, Johansson, 29, Knightley, 28, and Stone, 25, when she admonished: “Don’t grow up so fast. When you are in your 20s, look in your 20s…Girls in their 20s now are looking like they’re in their 30s.

“I would say enjoy your age… It flies by.”

And the actress spelled out to her pal exactly how to stay glam: “Girls like Jennifer and Keira should stay fresh-faced, keep their hemlines high, ditch those clunky outfit-killing shoes and avoid dressing in a famous designer’s clothes just because they are famous designers.

“Young Hollywood is growing up so fast, but they don’t have to rush it with outfits that are way beyond their years. They should revel in their youth – they’ll have plenty of time to rein it in when they’re older.”