By EDDIE PELLS
AP National Writer
ZHANGJIAKOU, China (AP) — American snowboarder Nick Baumgartner remembers the exact time he started feeling old. It was noon on Dec. 17, 2017 — his 36th birthday. He was racing in Austria and got tangled up in a jump. He broke three vertebrae in his back and said it took a lot more work to get back than it had when he was younger. Baumgartner is 40 now. On Thursday, he’ll kick off action at his fourth Olympics. He’s adding himself to an ever-growing list of older athletes still mixing it up in a young person’s sport. His sport, snowboardcross, is as rough as anything on snow. Baumgartner, a staple of the U.S. team since 2005, has had two World Cup podiums over the last three months.