Both mating system and diet are thought to drive inter-individual variation in bite force. Although previously published data suggest that bite force variation may be driven by variation in morphology (e.g. head morphology, body size, muscle size), age and physiology (e.g. fluctuating plasma testosterone levels) in some vertebrates, this remains untested in primates. Here, we explore the proximal determinants of bite force capacity in the grey mouse lemur Microcebus murinus. Our results show that in male grey mouse lemurs, bite force measurements are repeatable across a 1-month period. Yet, bite forces were independent of fluctuation plasma testosterone levels. Head dimensions and body mass were all positively correlated with bite force. Among these, head width was the best predictor of bite force as has been observed for other vertebrates. Unexpectedly, age was highly significantly and positively correlated with bite force. Whereas older animals generally bit harder, the oldest age group (5.5 years) showed a decline in bite force capacity. These results suggest that bite force in the grey mouse lemur is mostly determined by morphology and age, yet is independent of variation in testosterone. Future studies including a broader age range and animals of different sexes would be of interest to better understand the variation in bite force in this small lemur.