A World War II veteran from Mesa, Arizona, celebrated his 97th birthday this week.And in doing so, he lent credence to his theory that a key to staying young and living a long life is pushing your body to its limit."It works and I recommend it for anybody that wants to live to be one hundred, and I will," Dave Keaggy told KNXV on his 97th birthday.To mark the occasion, he completed a feat of strength. Challenging himself has been a birthday tradition the U.S. Air Force veteran has maintained for many years. It started in his 20s when he dared himself to complete 85 push-ups in under one minute. "I've been doing something like that ever since, and that's a long time ago," Keaggy said.The tradition has carried on in different ways. When he turned 70, Keaggy jumped out of an airplane. At 82, he bench-pressed 225 pounds, and for his 90th birthday, he did dozens of push-ups, KNXV reported.To mark his birthday this year, Keaggy set out to carry 100 pounds as he walked 100 yards. With two dumbbells in hand — and with 15-pound weights strapped around his ankles — Keaggy made his birthday fitness wish come true by walking at Mountainside Fitness in Mesa, Arizona. After conquering this year's birthday goal, Keaggy blew out the candles on his birthday cake and celebrated with a crowd that formed at the fitness center to cheer him on as he completed his feat of strength.See more in the video player above