No, they are not running at 25K RPM. They are variable speed and may have the capability of running at 25K RPM, depending on trigger position, available maximum voltage, design and manufacturer's specific characteristics.
Take two identical motors. One is connected to a power source that is higher voltage than the second identical motor. The mechanical loads are fixed/the same. The motor that is powered from the higher voltage source can run at a higher speed if commanded/higher voltage applied. This also assumes that the motor's torque requirements are less than or equal to the motor's capacity as well as the power source's ability to deliver current (produce torque). ie; the motor is not overloaded mechanically.
Yes, torque is proportional to current in both/either case(s). And yes, maximum attainable motor speed is dependant on number of poles, maximum applied voltage and winding design.