The Lansing effect predicts a decline in offspring performance with increasing maternal age. Maternal age and diet are both known to shape offspring development through maternal effects, but their combined influence is still poorly understood. This study investigated how maternal age at oviposition and maternal dietary conditions interact to influence offspring developmental plasticity in a thelytokous predatory mite, Amblyseius herbicolus Chant. Specifically, we asked: (i) how maternal age affects offspring developmental time and size at maturity, and (ii) whether maternal diet modifies the influence of maternal age on offspring performance. Mothers were maintained under either restricted or abundant prey diets (20 mothers per treatment), creating contrasting nutritional environments. Offspring produced at different maternal ages were then exposed to a gradient of prey availability to assess developmental plasticity (27–41 offspring per prey level). We monitored multiple life-history traits, including hatching success, survival to adulthood, developmental time, body size at maturity, and prey consumption during development. This design allowed us to evaluate both direct effects of maternal age and diet and their combined influence on offspring responses to environmental variation. Our findings provide evidence for an inverse Lansing effect. Offspring of older mothers exhibited higher survival and lower prey consumption during development, without any reduction in body size at maturity. Maternal diet modified these age-related patterns, with significant interactions observed for offspring prey consumption and developmental plasticity. Notably, offspring from older mothers maintained under restricted diets achieved the strongest overall developmental performance, suggesting that maternal age can mitigate potential constraints associated with limited resources. These results indicate that maternal effects are dynamic and vary with both maternal condition and reproductive timing. Maternal age emerged as a key determinant of offspring developmental trajectories, shaping how individuals respond to resource environments. The interaction between maternal age and diet underscores the importance of considering multiple maternal factors simultaneously when evaluating offspring performance. Overall, this study demonstrates that maternal age and diet jointly structure offspring development and highlights the need to incorporate maternal age into studies of maternal effects, life- history variation, and phenotypic plasticity.