Which of the following characteristics is a risk factor for myocardial infarction in women?

Increasing age is indeed a significant risk factor for myocardial infarction in women. As women age, particularly after menopause, the protective effects of estrogen decline, leading to an increased risk of cardiovascular diseases, including heart attacks. The incidence of myocardial infarction rises substantially in postmenopausal women, making age a critical factor in assessing risk.

While other options might seem relevant to various aspects of women's health, they do not directly correlate with a higher risk for myocardial infarction in the same way that increasing age does. For example, being premenopausal generally offers some level of protection against heart disease due to higher estrogen levels. Family history can influence risks across the lifespan but is less definitive compared to the universal impact of aging. Breast cancer, while a serious health concern, is not a direct risk factor for myocardial infarction. Instead, its associations may be linked to treatment factors rather than a direct physiological risk like age-related changes.