While HCI researchers have begun designing personalised VR experiences for older adults, there has been limited research examining the use of social VR -where users interact via avatars in a virtual environment. Avatar-mediated communication (AMC) is a crucial component of the social VR experience, but older users' experience with AMC is poorly understood. We conducted a five-month study with 16 older adults evaluating a co-designed social VR prototype. Results show that AMC in social VR was seen as medium that supported introverted users to express themselves and was viewed as offering advantages when discussing sensitive topics. Our study provides new insights into how older adults view AMC in social VR as a communication medium and we contribute six design reflections, based on our results, that highlight the steps that can be taken to ensure that AMC in social VR can meet the communication needs of older users.