Final answer:
Testicular atrophy typically occurs during old age, (option b) associated with a decline in Leydig cell activity and a consequent reduction in testosterone levels that lead to andropause, or male menopause.
Step-by-step explanation:
Testicular atrophy or degeneration typically occurs during old age. As males age, especially from 40 to 50 years onwards, there is a decline in Leydig cell activity which leads to a reduction in circulating testosterone levels. This condition is known as andropause or male menopause, and while less dramatic than the estrogen decline in women, it can still have significant effects. Symptoms of andropause may include fatigue, depression, anxiety, reduced muscle mass, loss of libido, insomnia, and sexual dysfunction. In old age, spermatogenesis also decreases, which can result in reduced sperm count and motility, affecting fertility.
Furthermore, primary or secondary deficiencies in male hormones can lead to atrophy of sex organs later life. It's important to note that testicular atrophy is not associated with puberty, strenuous physical activity, or as a direct result of hormonal therapy although certain hormonal therapies can have side effects such as testicular atrophy.