The factor that does not influence individual consumer buying decisions among the given options is 'Family', since it is a social not an individual factor, which includes relationships and external influences.
Out of the options provided, the factor that does not influence individual consumer buying decisions is 'C) Family'. While gender, age, personality, and life cycle stage are all individual factors that affect how consumers make purchasing choices, family is considered a social factor rather than an individual one. Individual factors are inherent to the person and are a part of their intrinsic characteristics or phases in life.
In contrast, social factors such as family involve relationships and external influences that affect buying behavior. The included reference material suggests that factors like tastes, preferences, income, and the size or composition of the population can influence consumer demand. These align with individual or economic characteristics that drive purchasing decisions.
So, 'Family' does not fall under the category of individual factors influencing consumer purchasing decisions, as it represents a social dynamic influencing consumer behavior.