When is permission from parents required for Jihad, and is permission waived if the parents are young or wealthy?

The default ruling for Jihad is that it is Fard Kifaya (a collective obligation). Permission from Muslim parents is required for Jihad if it is not an individual obligation, based on the Prophet's (peace be upon him) saying: "Are your parents alive? He said: Yes. He said: Then strive in their service." However, if Jihad becomes Fard Ayn (an individual obligation), then permission is not required, such as when a Muslim is present on the battlefield, or when the enemy invades Muslim lands, or when the Imam designates him for combat.