Background: Satisfaction with life is considered the best indicator of the quality of life of older people and is commonly used as an indicator of adaptation and successful aging. The objective of this study is to evaluate the quality of life and health among pre-seniors and seniors in Płock, Poland, focusing specifically on the interplay between life satisfaction and health outcomes. Methods: The study encompassed a total of 2040 individuals, categorized as pre-seniors and seniors. A diagnostic survey method was employed, utilizing a questionnaire that gathered sociodemographic data and incorporated two standardized psychometric scales: the Satisfaction with Life Scale (SWLS) and the Health Behaviours Inventory (HBI). Results: A majority of respondents demonstrated high levels of life satisfaction, with 1272 people (62.4%) scoring in the high range. In contrast, a smaller group, consisting of 299 respondents (14.7%), reported low satisfaction levels. Notably, men exhibited higher life satisfaction than women (p < 0.001). Additionally, a statistically significant but low correlation was found between the age of respondents and various aspects of the health behaviour index. This includes preventive behaviours (p < 0.001, r = 0.105), health practices (p < 0.001, r = 0.243), proper eating habits (p = 0.004, r = 0.063), and a positive mental attitude (p < 0.001, r = 0.098). These findings underline the complex interplay between age, life satisfaction, and health behaviours among the senior population. Conclusions: High life satisfaction and average to high levels of health behaviours were observed in our study, varying with gender and age. Individuals aged 61–75 reported the highest life satisfaction, whereas those aged 76–90 exhibited the most robust health behaviours. These results underscore the need for age- and gender-specific health policies and programs supporting sustainable aging, aligning with the Sustainable Development Goals. Further national research is essential to comprehensively explore these trends and support global well-being initiatives for aging populations.