We will be running motor at 50-60rpm, 90% of the time.
Measured the RMS current as 212mA and voltage as 8.7V.
The above shows that the test condition is less than the rated, will the motor life increases?
We are testing at 150rpm (5% of the time in our application) which is beyond the rated specification, the voltage -12.74V and current- 334mA. Will the motor and lifetime gets affected?
Our general recommendation for brushed DC motor operation is 25% or less of the stall current. For our 34:1 Metal Gearmotor 25Dx52L mm MP 12V, that means keeping current draw below 450mA, so your conditions seem appropriate for ensuring a good motor lifetime.
What will be the lifetime of these motors?
Unfortunately, we do not have our motor or gearbox lifetimes well characterized, and the lifetime will generally depend a lot on the specifics of your application, so that is something you would probably have to test for yourself in your actual system (perhaps in some accelerated way).