Unique among malignancies, age is a key prognostic indicator for well-differentiated thyroid cancer. Patients aged <45 years can have the same degree of disease involvement and a distinctly different prognosis than those aged >45. Although the reason for the association between age and outcome is not entirely clear, it does imply that there is something intrinsic to either the cancer or the treatment that is age dependent. This article explores the characteristics of the normal thyroid and thyroid cancer that are age dependent. It then provides theories for the relationship between advanced age and poor prognosis, in addition to treatment options tailored to age at diagnosis.