Brushed DC motor as generator, characterising the motor
"100-6000 rounds" probably means 100-6000 revolutions per minute. Used as a generator, the motor will probably produce about 5.5/6000 = 0.0009 volts per RPM. I assume speed in Hz is equivalent to revolutions per second. The voltage produced should be 0.0009 X 60 = 0.055 V or 55mv per RPS. At 12 revolutions per second, you could expect about 55 x 12 = 660 mV.

If the motor/generator produces 5.5 V and 100 mA at 6000 RPM that would be a maximum power of 100 X 5.5 = 550 milliwatts.

You can calculate torque from Power(W) = T(Nm) X RPM X 2Pi/60