Background and Objectives: Aging is a biological and irreversible process characterized by physiological alterations resulting in a progressive decline in biological functions, decreased resistance or adaptability to stress, and increased disease susceptibility. A decline in functional fitness, imbalance between pro- and antioxidant capacity, and/or hormonal dysregulation adversely impact physical capacity, emotional status, and overall quality of life, especially within the elderly population. On the other hand, regular physical activity is considered an effective strategy to prevent and reduce those changes associated with primary aging and concurrent chronic disease, while slowing age-related physical degeneration. However, there is still limited evidence-based information regarding both the intensity and interval of effective interventions on physical functioning in older adults. Thus, the aim of the study was to assess the effects of a 24-week regular multimodal exercise program on functional fitness, oxidative stress, salivary cortisol level, and self-perceived quality of life in a group of eighteen physically active elderly subjects (mean age 72.8 ± 7.5 years). Materials and Methods: A set of anthropometric and physical measurements (grip strength, chair sit to stand, sit and reach and back scratch) assessing the functional fitness performance were evaluated. Moreover, biochemical markers (derived-reactive oxygen metabolites (d-ROMs) and the biological antioxidant potential (BAP) tests, and salivary cortisol levels) and the EuroQoL 5-Dimension 3-Level (EuroQoL 5-D 3-L) self-perceived questionnaire of quality of life were measured before and after the intervention program. All measurements were normally distributed as assessed by D'Agostino and Pearson's omnibus normality test. Student's t-tests were used to evaluate the differences in all the parameters measured at baseline (T0) and after the 24-week physical program (T1). Results: The results showed that an age-tailored structured intervention exercise program (1 h per session, twice per week, for 24 weeks) was effective in improving flexibility and other biomechanical parameters, such as muscle strength and the dynamic balance fitness component, which are key to performing daily tasks independently. Moreover, biochemical analyses demonstrate that the proposed intervention program has beneficial effects on the balance between plasma ROS production and their neutralization. Conclusions: The results confirm the benefits of regular physical activity in older adults resulting in improved physical strength and flexibility in the functional fitness parameters, and in regulating anti- and pro-oxidant activity and cortisol (stress hormone) levels.