Age data are fundamental to ecological studies and species management. However, age determination of the corallivorous crown-of-thorns seastar (CoTS; Acanthaster spp.) has been challenging in the past due to their extreme plasticity in growth, difficulties in tagging and identifying individuals, and a lack of reliable size-independent proxies of age. The inability to resolve the age of CoTS has hampered our understanding of their population dynamics. Thus, this research aims at exploring a molecular approach to determine the chronological age of CoTS. Telomeres are non-coding DNA sequences found at the ends of eukaryotic chromosomes, which continue to shorten throughout life and serve as proxy of age in wild animals. While telomere dynamics is highly species-specific, it is under-explored in marine invertebrates. Here, we quantify the telomere lengths in CoTS of a range of known age, from newly settled individuals to mature adults that are >2 years old. We investigate the correlation between age and telomere length, as well as the influence of diet and tissue type on telomere dynamics of CoTS. The results of this study will enable us to determine whether telomere length is a suitable marker for age determination in CoTS.