56-year-old Kerstin Tristan, a mother and grandmother from Germany, once hated tattoos—until 2015, when she decided to try something new. “We only live once,” she said. “At my age, something real had to come.” That first tattoo completely changed her perspective. Since then, Kerstin has spent around €30,000 (about $32,000) covering her body in vibrant ink. Her designs include roses...