The detrimental effects of lockdowns have already been proven by numerous studies, mainly using psychometric measurements. Since telomere shortening is a driver of aging and aging-associated disorders, including cognitive decline, the telomere length in the older population has been investigated in the current study. Measurements were taken over a 6-month period just before and during the 6 months that included the first lockdown. The cohort of 55 persons aged 64 to 70 years was investigated in the context of a study focusing on neuroplasticity. Participants were recruited in Germany and Switzerland and characterized by psychometric measurements concerning neurocognition and neuroplasticity. Telomere lengths were measured by real-time PCR-based LTL measurement. We found an impressive and significant decline in telomere lengths in the period that included the lockdown (2.33 (± 0.1) at T1 vs. 1.35 (± 0.1) at T2), whereas it was stable in the phase before the lockdown in the same individuals (T0 was 2.25 (± 0.1 S.E.M.) vs. T1, 2.33 (± 0.1)). Correlation of the sudden decrease revealed no linkage to health issues or general physical activity but was in trend related to a decline in the WHOQOL-BREF Social Score referring to the social interaction of the study participants. Our data support, at a biological level, the results of clinical and psychosocial studies showing the detrimental effects of lockdowns.