Obesity is a testosterone-sapping culprit, so losing a few pounds could help an overweight man regain normal testosterone levels. Other underlying causes of low testosterone may be as serious as cancer or immunosuppression. The Mayo Clinic estimates that up to 30 percent of men aged 70 and older suffer from low testosterone, but the treatment for the condition is debatable. Medication can help some cases of low testosterone. In other cases, the irritability may just be a byproduct of a changing lifestyle such as retirement. When major life changes affect men, it's natural for them to feel apprehensive and even angry about it. Take a double-pronged approach to your grouchy guy: Get him in for a physical, and see if you can open the lines of communication.