Retirement age exists because at one time it was expected that people would generally achieve a certain level of wealth and live out the rest of their days doing what they wanted with that wealth and time.

A retirement age exists because it was fought for by the labor movement, and it was set during the creation of Social Security in the US during the New Deal. It was also set at the average age of death IIRC, and because a large part of the homeless problem during the Great Depression was seniors who had not saved enough money to support themselves without a job’s income and were largely unable to obtain new work.