Ceylon cinnamon (Cinnamomum zeylanicum), a native spice of Sri Lanka, is rich in bioactive compounds known for their potent antioxidant properties, which contribute to various health benefits such as anti-diabetic, anti-cancer, lipid-lowering and anti-inflammatory effects(1). However, the concentration of these bioactives can fluctuate throughout the plant’s life due to internal and external factors such as light, temperature, and stress responses. This study aimed to investigate the changes in total phenolic content (TPC), total flavonoid content (TFC), and the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity at different stages of maturity (1st to 4th year), using two extraction methods: ultrasonic extraction and accelerated solvent extraction. The identification and quantification of key bioactive compounds, including cinnamaldehyde, eugenol, and cinnamic acid, were performed using high-performance liquid chromatography (HPLC). The accelerated solvent extraction proved to be more effective in extracting TPC, TFC, cinnamaldehyde, eugenol and inhibiting DPPH. The extracts obtained from the accelerated solvent extractor showed a notable decrease in TPC (from 55.89±4.28 to 14.12±0.75 mg/g gallic acid equivalent) and TFC (from 170.08±13.75 to 39.35±9.39 mg/100g quercetin equivalent) up to the 3rd year, followed by an increase in TPC (from 14.12±0.75 to 19.71±0.49 mg/g gallic acid equivalent) and TFC (from 39.35±9.39 to 68.82±9.44 mg/100g quercetin equivalent) thereafter. The highest and lowest DPPH inhibition of 85.30 ± 0.39% and 40.68 ± 1.08% was observed with the 1st year and 3rd year plants. There was no significant difference between the DPPH inhibition of the 2nd and 4th year plants (p>0.05). The highest yields of eugenol (18.2485±0.02 mg/g of dry weight) and cinnamaldehyde (22.1475±0.024 mg/g of dry weight) were observed in the 3rd-year plant extracts obtained via accelerated solvent extraction. Conversely, the highest yield of cinnamic acid (0.4161±0.00 mg/g of dry weight) was found in 4th-year plants extracted using ultrasonic extraction. A statistically significant correlation was observed between cinnamaldehyde and eugenol content (p<0.05, R²=0.992), TPC and cinnamic acid (p<0.05, R²=0.906), and TFC and cinnamic acid (p<0.05, R²=0.956) across all ages. This study offers valuable insights into the variation of essential bioactive compounds in cinnamon as the plant matures, facilitating the optimization of its applications.