When She Celebrated Her 21st Birthday in a Slinky Silver Ensemble Yes, Kendall celebrated her 21st birthday in a plunging minidress, and yes, it was covered in Swarovski crystals. A year after she wore the dress in 2016, the Kendall + Kylie clothing line released its own, more affordable version. Image Source: Getty / wowcelebritytv/Bauer-Griffin