The objective of this study was to measure the mRNA expression of four myogenic regulatory factors in the sirloin of Czech Fleckvieh heifers and bulls during their postnatal growth and estimate its association with sex and age. The sex and age of animals significantly influence the expression activity of myogenic factors. In heifers, the expression of myogenic factors is higher compared to bulls during growth. In bulls, on the other hand, it is more balanced through the whole evaluated period. The age-sex interaction influences more only the expression of the myogenin gene. The most statistically significant differences were recorded among the particular levels of age and gender interactions and the gene expression of the myogenic differentiation factor 1 and myogenic factor 6. The study provided new insights into the importance of myogenic factors for regulating muscle metabolism, growth potential, and the development of bovine meat performance traits.