The factor likely to have the greatest positive influence on an individual's development of lifelong healthy physical and nutritional habits is:

Growing up in a household where health habits were valued lays a foundational influence on an individual's development of lifelong healthy physical and nutritional habits. This environment typically provides consistent modeling of healthy behaviors from parents or caregivers, which can instill a sense of the importance of health and nutrition from an early age.

When children observe their family prioritizing healthy eating, regular physical activity, and active discussions about health choices, they are more likely to adopt these practices as their own. Family dynamics play a crucial role in shaping attitudes and behaviors; thus, individuals raised in such homes may carry these values into adulthood, leading to sustained healthy habits.

In contrast, while access to health education programs, participation in community wellness activities, and exposure to health-related media are all beneficial for promoting healthy behaviors, they may not have the same depth of influence as the early and consistent modeling of health habits within the family. These external factors can supplement and reinforce health knowledge but may not instill the same ingrained values that come with growing up in a health-oriented household.