A challenge facing engineering with natural fibers is the high standard deviation of mechanical properties of natural fiber compared with synthetic fiber. Plants have a chemical and physical architecture reflective of their age. The region near the apex is more flexible than that near the base. In this paper we investigate the impact of increasing age of plant fiber on the corresponding composite. Bast fibers stems of kenaf (Hibiscus cannabinus, L.), a warm season tropical herbaceous annual plant extracted corresponding to different age, were dispersed into Poly‐l‐lactide (PLLA) matrix by melt blending followed by compression molding. The resulting bio‐based hybrid composites were characterized by X‐ray diffraction (XRD), attenuated total reflectance‐Fourier transfer infrared spectroscopy (ATR‐FTIR), differential scanning calorimetry (DSC), optical microscopy (OM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were conducted. DSC and XRD indicated that the kenaf was effective in promoting crystallization. TGA indicated that the thermal stability of composites is reduced compared with PLLA, but the older fiber sample based on 120–150 cm from the plant apex improved thermal stability compared with the rest. SEM and OM inferred good fiber dispersion while dynamic mechanical tests revealed increased modulus. POLYM. COMPOS., 35:915–924, 2014. © 2013 Society of Plastics Engineers