It is true that testosterone levels become lower as men age, but it's also true that many men continue to achieve erections despite this decline. In fact, according to a Harvard Medical Report on erectile dysfunction, a man with virtually no testesoterone might still be able to have an erection. Moreover, in a large study of older men, researchers found no connection between erectile function and levels of sex hormones. So the answer isn't that simple. However, if you suspect low testosterone levels, a Urologist will be able to guide you.