My Father Is 88 Years Old And Has Been An

My father is 88 years old and has been an avid walker his whole life on a daily basis. Fairly active on a regular basis. In the last month he has been complaining about strong lower back pain, pain on each side of his stomach. He is loosing his appetite and is loising his energy. My sister feels it may be prostate problems, yet he is not experiencing any urinary problems or change. Any thoughts with regards to his age and these symptoms?