Globally, 77\% of the elderly aged 65 and above suffer from multiple chronic ailments, according to recent research. However, several barriers within the healthcare system in the developing world hinder the adoption of home-based patient management. IoMT is beneficial for healthcare personnel, but its application raises security concerns, particularly in authentication. Several authentication techniques have been proposed which, however, lack a balance of security and usability. By analyzing the shortcomings of the existing authentication methods and the available sensors on smartphones, this paper proposes to explore the possibility of using a smartphone’s embedded sensors for elderly user identification process in IoMT. We proposed an adaptive authentication technique for the elderly patients using the MAPE-K$_{\text{HMT}}$ framework by developing an android application that takes as input, the user’s contextual information including device fingerprint, location, network, and user data to monitor the user and estimate the risk associated with a user using the Naïve Bayes algorithm. The risk score was then used as input to the rule-based module that assigned authenticators according to user age, health condition and available authenticators. The model demonstrated high accuracy in distinguishing between authorized and unauthorized access attempts and supported the usable security goal for the elderly users.