A function that runs for each agent in each period and increments the agent’s age by 1. This function should not be called directly, but should be hooked using
WARNING: This is an internal function. Its use in user code is not recommended or supported, and its signature can change in future updates without warning. Use one of the suggested functions above instead, if applicable.
stage — int, required
Multi-stage models will call agent step functions multiple times per period. This argument is passed indicating which stage of the period the model is currently in.