She regularly keeps her 135 million Instagram followers abreast of her newest diet and exercise tips. And Kourtney Kardashian was at it again on Monday when she shared some of her favorite exercise routines featuring a workout ball. The 42-year-old former Keeping Up With The Kardashians star looked years younger than her true age a she showed off her sculpted abs while working out with her youngest sister Kylie Jenner. Incredible shape: Kourtney Kardashian, 42, flashed her sculpted abs in an Insta Stories photo shared Monday as she worked out at the gym with her sister Kylie Jenner, 23 Kourtney was spotted in the background of the wood-floor gym in a black sports bra and high-waisted black leggings that still showed off plenty of her toned tummy.