I have seen extensive information on the origin,variants,behaviour,and Enclave exploitation of deathclaws,but I have never once heard how long they live if you never blow thier heads off. Would anyone know the natural life expectancy of a deathclaw? Please,it's been driving me crazy!
Deathclaw origin is the result of pre-war experimentation on Jackson's Chamelions, as has already been mentioned above. They don't vary as far as the species goes, Deathclaws had fur in Fallout: Tactics, but this can be considered an inconsistency. They are very aggressive, agile, and deadly (though you only need to play any of the Fallout titles to learn that). The Enclave performed post-war experiments on Deathclaw specimens to try and augment their intelligence with a strain of F.E.V. This was very successful, albeit too successful, as the intelligent Deathclaws learned of their purpose to be used as weapons by the Enclave, and then played dumb, leading the Enclave to believe they wouldn't become an uncontrollable threat. This unique deathclaw pack was sought out and exterminated. Since then the Enclave have introduced a mind control system to tame the Deathclaws, which you see in Fallout 3.
As for life expectancy, this has never been covered. But they are very fertile, and are loyal to their packs. Add that to their toughness and aggression, and you get a very adaptable and survivable combination.