Purpose: To investigate the influence of age and time since edentulism on masticatory function and quality of life related to oral health (OHRQoL) in totally edentulous patients after implant-retained mandibular overdenture (IMO) loading. Materials and Methods: The sample consisted of 33 patients categorized in two age groups (≤ 65 and > 65 years, respectively), and two time since edentulism groups ( 25 and ≥ 25 years). The masticatory function was evaluated through the masticatory performance and swallowing threshold tests before IMO loading, and 1, 3, 6, and 12 months after IMO loading. The OHRQoL was evaluated by applying the Oral Health Impact Profile (OHIP-EDENT) and Geriatric Oral Health Assessment Index (GOHAI) questionnaires, before loading and after 3, 6, and 12 months. Data were subjected to the Mann-Whitney test and Wilcoxon signed-rank test for paired samples. Results: The masticatory performance and swallowing threshold were not influenced by the age nor by time since edentulism, except 6 months after IMO loading when patients ≤ 65 years of age performed the swallowing threshold test in a significantly shorter time with a reduced number of masticatory cycles (P .05). The masticatory performance and swallowing threshold outcomes showed a gradual improvement up to 12 months, irrespective of the patient categorization. The GOHAI questionnaire scores showed that the OHRQoL was influenced by age in complete denture wearers with a difference between groups in the psychosocial and global domains. The time since edentulism was not affected by the GOHAI scores of complete denture wearers (P .05). The OHIP-EDENT questionnaire only indicated significant differences as a function of age or time since edentulism between complete denture wearers. Age was associated with significant differences in the physical pain domain outcome, while time since edentulism did not affect only the psychologic discomfort, psychologic inability, and handicap domains. Conclusion: Neither the age nor the time since edentulism influenced the masticatory function of IMO-wearing patients. However, IMO significantly improved the masticatory function in totally edentulous patients, and this is more evident for younger patients (≤ 65 years) with a shorter time since mandibular edentulism ( 25 years). The OHRQoL is only influenced by age and time since edentulism in complete denture wearers; IMO treatment eliminates these differences. Keywords: edentulism, masticatory function, overdentures, quality of life, totally edentulous patients