flaps 25 is still a takeoff setting...
cut and pasted from current 737-800 manual
Takeoff configuration warning is armed when the airplane is on the ground and either or both forward thrust levers are advanced for takeoff. Takeoff
configuration warning activates if:
• trailing edge flaps are not in the flaps 1 through 25 takeoff range, or
• trailing edge flaps are in a skew or asymmetry condition, or have
uncommanded motion, or
• leading edge devices are not configured for takeoff or have uncommanded
motion, or
• speed brake lever is not in the DOWN position,
as regarding the configuration warning with ldg gear NOT down:
Flaps 15 through 25 –
• either forward thrust lever set below approximately 20 degrees or an
engine not running, and the other thrust lever less than 34 degrees; thelanding gear warning horn cannot be silenced with the landing gear
warning HORN CUTOUT switch.