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The interest in the effect of genotype by environment interaction (GEI) is increasing because animal breeding programs have become geographically broader. Climate changes in the next decades are also expected to challenge the present breeding goals, increasing the importance of environmental sensitivity. The aim of this work was to analyze GEI effect on cattle weight using the environmental sensitivity predicted by random regression reaction norm models, including sex and age effects as additional dimensions in the study. Genetic parameters were estimated for adjusted weights of Brazilian Nelore cattle at different ages (120, 210, 365 and 450 days), using linear polynomials for random regression analysis. The analyses with sex as a fixed effect (total analyses - TA) were compared to those with sex-separated progenies (male and female progeny analyses - MPA and FPA, respectively). (Co)variance components were estimated and breeding values calculated as expected progeny differences (EPDs). The results showed important differences in reaction norm model genetic parameter estimates according to different age and sex analyses. They confirmed the presence of an important genotype by environment by sex by age interaction for Nelore cattle weight. The patterns in these results lead to a revision of the importance of sexual and developmental factors on plasticity and adaptation concepts. [ABSTRACT FROM AUTHOR]