What is an 80 year old called?

Anyone who is in the 80s is called an Octogenarian



oc·to·ge·nar·i·an (ŏk'tə-jə-nâr'ē-ən)
adj. Being between 80 and 90 years of age.
n. A person between 80 and 90 years of age.

[From French octogénaire, from Latin octōgēnārius, containing eighty, from octōgēnī, eighty each, from octōgintā, eighty : octō,eight