This study aimed to evaluate the effect of sex and sub-zero storage temperature on the microbial and oxidative stability of Belgian Blue beef packed in a high-oxygen atmosphere after different ageing times. Longissimus thoracis et lumborum from Belgian Blue young bulls and cull cows were aged at −1 or 4 °C for 80 days in vacuum. Every 20 days, samples were repackaged in a high-oxygen atmosphere (70/30% O2/CO2) and stored for 7 days (2 days at 4 °C + 5 days at 8 °C). Ageing at −1 °C had a protective effect against the growth of lactic acid bacteria and Enterobacteriaceae and myoglobin oxidation. Brochothrix thermosphacta was the limiting parameter for ageing longer than 20 days at −1 °C, permitting a subsequent 7-day shelf-life in a high-oxygen atmosphere. Meat from young bulls was more sensitive to oxidation than meat from cull cows. Extending Belgian Blue meat ageing for >20 days had a negative impact on retail shelf-life. •Ageing at −1 °C can improve microbial and colour stability of meat.•Meat from young bulls is more sensitive to oxidation than meat from cull cows.•Brochothrix thermosphacta growth limits the length of beef ageing at −1 °C.•Ageing Belgian Blue meat for >20 days is not recommended for retail display.