Polysaccharide, the main component of Polygonatum kingianum, has been proven to have many pharmacological effects, such as antioxidant, anti-aging and anti-bacteria. The accumulation of polysaccharides was greatly influenced by the growth age of P. kingianum. Therefore, a fast and low-cost chemometric method is needed to identify the growth age. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) and ultraviolet visible (UV-Vis) spectroscopy of P. kingianum with four growth ages (80 samples) were collected and analyzed by chemometric methods. The correlation between 13 agronomic traits and polysaccharide accumulation was discussed. A data fusion strategy was used to identify the growth age of P. kingianum by extracting the latent variables (LVs) and principal components (PCs) of the spectra. The results founded that the polysaccharide content showed a negative correlation the fibrous root number, leaf length, leaf width, stem diameter and fresh weight on the ground part. The ATR-FTIR and UV-Vis spectra in P. kingianum with different growth ages were similar. The regions of 1750–1500 cm−1, 1000–750 cm−1 and 200–250 nm, 330–360 nm are important variables for discriminating four growth ages of P. kingianum. The classification effect of data fusion models was better than that of single spectra models with 100% accuracy as well as perfect sensitivity and specificity. Hierarchical cluster analysis shown that the samples were divided into two categories: one 5-year-old and the other 2, 3 and 4-year-old. In summary, the polysaccharide content in 4-year-old P. kingianum by seed reproduction was the highest. Data fusion of ATR-FTIR and UV-Vis spectra combined with PLS-DA models could be used to accurately distinguish P. kingianum in different growth ages, which was valuable for the identification and evaluation of other medicinal and edible homologous plants. Meanwhile, it also provides a theoretical basis for the harvesting age and cultivation conditions of P. kingianum.