This work investigates the service rate allocation (SRA) for age of information (AoI) minimization in a dual-sensor monitor system where two sensors update status of two processes to a common monitor collaboratively. Both sensors sample and generate updates of the two processes by following a zero-wait discipline and transmit the updates to the monitor with exponentially distributed service times using service rate allocated to each process. Aiming at minimizing the maximal peak (average) AoI of the two processes, the optimal SRA problem is boiled down to a one-dimensional search in a short interval, which can be quickly found by bisection method. Accordingly, a closed-form suboptimal SRA is also proposed, where it requires the sensor with less service rate to monitor only one process. Numerical results validate the effectiveness of the suboptimal scheme in achieving the optimal AoI.