ur clone's DNA is still ur old DNA. for example, u're using ur DNA to clone urself at 40 yr old. after 30-40 yrs, u die, and ur clone will probably die that time.

the telomeric region decreases after each cell division. so when no telemores to loss, the important part of the DNA will be loss.
this is just a theory though. it can be use to explain why Dolly die so early.