The artist formerly known as Tiffani Amber Thiessen has grown up into a more Tiffani Thiessen: What’s under that White Kelly Kapowski in the high. January 23, Tiffani-Amber Thiessen is 40(!) years old today, so we're looking back at Kelly Kapowski--and other memorable roles! Tiffani Amber Thiessen (born January 23, ) is an American actress. She is known for starring as Kelly Kapowski on NBC's Saved by the Bell (–93) and as Valerie Malone on Fox's Beverly Hills, (–98), Born: January 23, (age 44), Long Beach, California, U.S.