One can use the Principle of Extremal Aging to calculate the path of a freely moving body (in an inertial frame not subject to any forces) in spacetime, curved or flat. Why extremal? Why not just maximal? All the examples I know of involve maximum proper time for a freely moving body. For example the twin paradox. The earth is the freely moving body and the stay at home twin ages the maximum (ignore gravitational time dilation). Can anyone give me an example of minimal aging and explain the circumstances a freely moving body experiences this? How does minimal aging occur?