If a building sprinkler system has a sprinkler head of 50 years old is it still good?

It depends. NFPA states that sprinklers over 50 years of age should be replaced or should have a representative sample tested. This means that sprinkler samples need to be pulled from the system and sent to a testing laboratory (UL) for testing. If the sprinkers pass this test, a certificate is issued stating that the sprinklers are still operational.