Chronological age is one of the important factors influencing muscle development and meat quality in chickens. To evaluate the protein expression profiles during skeletal muscle development, we performed a tandem mass tag (TMT)-based quantitative proteomic strategy in pectoralis major (breast muscle) of Beijing-You chicken (BYC) at the age of 90, 120 and 150 days. A total of 1,413 proteins in chicken breast muscle and 197 of them were differentially expressed (fold change ≥ 1.2 or ≤ 0.8333 and p < 0.05). There were 110 up- and 71 down-regulated proteins in 120 d vs. 90 d group, 13 up- and 10 down-regulated proteins in 150 d vs. 120 d group. The proteomic profiles of BYC at 120 d were very similar to those at 150 d and highly different from those at 90 d, suggesting that 120 d might be an important chronological age for BYC. Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses indicated that these differentially expressed proteins were mainly involved in the pathway of glycolysis/gluconeogenesis, adrenergic signaling in cardiomyocytes, focal adhesion, oocyte meiosis and phagosome. Protein expression analysis indicated that the differences in muscle growth rate between ages were regulated by proteins such as LDHA and ENO3, whereas ATP2A1 and HSP70 were associated with water-holding capacity (WHC), and PPP1CB and COL1A2 were suggested to lie in the role of intramuscular fat (IMF) deposition. In addition, RACK1 was thought to be crucial for the sexual maturation during chicken development. Furthermore, some DEPs were quantified using parallel reaction monitoring (PRM) to validate the results from TMT analysis. Overall, the present work could strengthen our view of the temporal expression profile during development and identify novel biomarkers for genetic breeding of chickens.