Turn On, enable and active are the same thing. It's turned on, its enabled and it's active. If it's not active, then it's not turned on or enabled.
It is turned on individually for each Apple ID that is part of Family Sharing group. It is not a global setting for all Family Group members. If you turn it on for one member it's just turned on for that member, but not all other members.
The Family Organizer can turn on turn on, enable or activate Ask To Buy for Child accounts. But it can remain on if they grow into being an adult and is not manually turned off (it won't turn off on its own when they become adults). The Organizer cannot directly turn it on for Apple IDs belonging to adults but it will remain turned on if they were children and grew normally into an adult and never turned it off.
You can also turn it on if you change the age of the Apple ID of the adult back to a child, then return the age back to adult. It will remain activated.