The human gut is a reservoir for antibiotic resistance genes. In this report, we used a DNA microarray chip covering 369 resistance types to investigate the relationship between antibiotic resistance-gene diversity and human age. Metagenomic DNA from fecal samples from 124 healthy volunteers of four different age groups (pre-school-aged children (CH), school-aged children (SC), high school students (HSS) and adults (AD)) were hybridized to the microarray chip. The results showed that 80 different gene types were recovered from the gut microbiota of the 124 individuals: 25 from CH, 37 from SC, 58 from HSS and 72 from AD. Further analysis indicated that the antibiotic resistance genes in the CH, SC and AD groups clustered independently, whereas the gene types in the HSS group were more divergent. Our results indicated that antibiotic resistance genes in the human gut microbiota accumulate from childhood to adulthood and become more complex with age.