Background/Objectives: Advanced age in Parkinson's disease (PD) is linked to worse motor function, more severe symptoms, and impaired activities of daily living (ADLs). Lee Silverman Voice Treatment (LSVT)® BIG may be suitable for older patients, as it can be adapted to individual abilities. This study evaluated whether age affects the effectiveness of LSVT® BIG on gait speed, motor symptoms, ADLs, and quality of life (QoL) in PD. Methods: In this retrospective, single-center cohort study, 22 patients with PD were divided into an older group (≥65 years; n = 16) and a younger group (<65 years; n = 6). All participants completed 16 one-hour, face-to-face LSVT® BIG sessions. Gait speed was assessed with the 10-m walk test; motor symptoms with Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III; ADLs with MDS-UPDRS Part II; and QoL with the Parkinson's Disease Questionnaire-39 Summary Index. Two-way mixed-design analysis of variance with aligned rank transformation was used for statistical analysis. Results: Significant improvements were observed for all outcomes (gait speed, motor symptoms, ADLs, and QoL) after the intervention. A significant effect of age group was found for gait speed, with younger patients walking faster overall. No significant interaction between timepoint and group was observed for any measure. Conclusions: LSVT® BIG appears to improve gait speed, motor symptoms, ADLs, and QoL in patients with PD, regardless of age, suggesting it is an effective intervention for both older and younger patients.