Let’s not make this too complicated.  To clarify,

For all ages where we provide referees (U8 to U19),
On any kick “coming out” of the penalty area (goal kick, indirect free kick, direct free kick),
The defending (kicking) team may kick when ready unless the referee directs the kicker to wait (substitution, injury, etc.).
The opposing team must retreat behind the line (build-out line, penalty area line, depending on the age),
AND be ten yards from the ball.
If the kicker chooses not to wait, it is not an infraction for the opposing team to be too close.
The ball is in play (and may be challenged) as soon as it is kicked and moved.

The referee will not tell the kicker to wait until the opposing team has fully retreated, but the kicker may choose to wait.  If the opposing team is slow to retreat, the referee may:

Do nothing.
Encourage them with words to move along.
Blow the whistle, move them back, and restart with a whistle.  Rare.
Show a yellow card if this behavior continues.  Extremely rare.

The good news is that all those multiple re-do’s when the kicker could not kick the ball far enough to cross the line have now been eliminated.