Telomeres are protective caps at the end of chromosomes that shorten as cells divide over time. Shorter telomere length is considered a biomarker for aging and age-related diseases. A person's biological age, as measured by telomere length, can differ from their chronological age due to lifestyle habits, environmental factors, and genetics that influence telomere shortening. Understanding biological age through telomere testing allows for personalized health and lifestyle changes to slow the effects of aging.