Controlling weight and dietary intake are important for hypertensive patients to manage their blood pressure. However, the interaction effect of gender and age on weight and dietary intake is not well known. The aim of this study was to examine the main and interaction effects of age and gender on body mass index (BMI) and dietary intake in hypertensive patients. We analyzed data from 4287 participants with hypertension (1600 participants 45–64 years old and 2687 participants 65 years or older) who participated in the Korea National Health and Nutrition Examination Survey (2013–2016). Two-way ANOVAs were conducted to examine the main and interaction effects of age and gender on BMI and dietary intake. Gender and age had significant main effects on BMI, intake of energy, cholesterol, sodium, and potassium. However, both gender and age illustrated interaction effects on BMI (F = 8.398, p = 0.004), energy intake (F = 12.882, p < 0.001), and cholesterol intake (F = 6.107, p = 0.014), while not showing any significant interaction effects on sodium (F = 3.547, p = 0.060) and potassium (F = 3.396, p = 0.066). Compared to the middle-aged group, BMI, energy intake, and cholesterol intake decreased in the older-aged group. However, the declines were steeper in men than in women. Therefore, both gender and age need to be considered for weight and dietary intake management for hypertensive patients.