India's demographic landscape is undergoing a profound transformation as Generation Z women (born 1997-2012) navigate evolving socioeconomic priorities, resulting in unprecedented delays in marriage and childbearing. The average age at first marriage for urban Indian women has risen to 27 years in 2024, while the national Total Fertility Rate (TFR) has declined to 1.9, below replacement level. This demographic shift coincides with emerging lifestyle patterns, including increased alcohol consumption and smoking among young urban women, creating a complex intersection of delayed family formation and compromised reproductive potential. This article examines the tripartite relationship between late marriage, substance use behaviors, and reproductive health outcomes among Gen Z women in India. Drawing from National Family Health Survey (NFHS) data, clinical studies from Indian fertility centers, and demographic research, we analyze how smoking accelerates ovarian depletion and increases infertility risk, while alcohol disrupts endocrine profiles and ovulatory function. The study explores regional variations, with southern states like Kerala and Tamil Nadu exhibiting TFR as low as 1.3-1.5, contrasted with higher fertility in northern states. Evidence indicates that while Gen Z women prioritize education and career advancement, the compression of reproductive timelines combined with lifestyle factors contributes to rising infertility rates and expanding IVF markets (projected to reach USD 3.46 billion by 2033). This paper argues for culturally sensitive reproductive health education and policy interventions that address the temporal disconnect between social aspirations and biological constraints in India's rapidly transforming society.