Low testosterone Levels

Patient: What is considered to be a low level of testosterone. My sex drive is gone and i am always tired. I am afraid my wife is getting frustrated because of my dramatic decreased sex drive. I recently had my levels tested and the results revealed that my level was 355. Ive read that normal range is between 290 and 1100, which seems pretty wide of a range. It also states that the study range is determined by 20 through 80 year olds. Please help.