Thanks Alexander Lorenz for your explanation.

As cells divide overtime telomeres shorten and eventually cell division stop, Our cells replenish by copying themselves. This happens constantly throughout our lives. Telomeres get shorter each time a cell copies itself, but the important DNA stays intact. Eventually, telomeres get too short to do their job, causing our cells to age and stop functioning properly. Therefore, telomeres act as the aging clock in every cell.

whereas Subtelomeres are extraordinarily dynamic and variable regions proximal to telomere region Duplications among subtelomeres have spawned small gene families, making inter-individual variation in subtelomeres a potential source of phenotypic diversity..

Thanks Rosaiah Kotikalapudi  for your answer