Integrating the ultra-reliable and low-latency communication (URLLC) with massive access, the massive-URLLC (mURLLC) in the sixth generation (6G) wireless networks aims at providing a wide range of delay-sensitive real-time services and applications by satisfying users' stringent requirements on the delay-bound and error rate. The age of information (AoI) theory characterizes the freshness of information, which measures the time elapsed since the generation instant of the latest received information update, and thus, has been recognized to be able to analyze the time-critical information's transmission latency in mURLLC networks. However, how to accurately characterize the AoI for 6G mURLLC networks has neither been well understood nor thoroughly studied. To overcome this challenge, in this paper we propose and develop an analytical modeling technique to characterize the AoI to efficiently support mURLLC services over 6G mobile wireless networks. First, we develop a stochastic hybrid system (SHS) model to track the AoI's evolution in the M/M /k queueing mURLLC networks. Second, we analyze AoI dynamics in the proposed SHS model, including deriving closed-form expressions for moments of the AoI and the state probability. Third, we prove the Lyapunov stability of the AoI under our proposed SHS model. Finally, we validate and evaluate our derived results of the AoI evolution in mURLLC networks through numerical analyses.