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octogenarian
US
/ˌɑːk.toʊ.dʒəˈner.i.ən/
UK
/ˌɒk.təʊ.dʒəˈneə.ri.ən/
A person who is between 80 and 89 years old

Persian equivalent:
Example:
Only octogenarians and nonagenarians were allowed to join that committee for the elderly.