How is telomere length maintained?

Telomerase is only found in very low concentrations in our somatic cells. Because these cells do not regularly use telomerase, they age leading to a reduction in normal function.
The result of aging cells, is an aging body.
Telomerase is found in high levels in germ line cells (egg and sperm) and stem cells. In these cells telomere length is maintained after DNA replication and the cells do not show signs of aging.
Telomerase is also found in high levels in cancer cells. This enables cancer cells to be immortal and continue replicating themselves. If telomerase activity was switched off in cancer cells, their telomeres would shorten until they reached a ‘critical length’. This would, prevent the cancer cells from dividing uncontrollably to form tumors.
The action of telomerase allows cells to keep multiplying and avoid aging.