When was congenital-analgesia (aka congenital insensitivity to pain), the inability to feel pain, clinically documented?
It was first reported in 1932 in this paper:
Dearborn, G. V. N. (1932). A case of congenital general pure analgesia. Journal of Nervous and Mental Disease, 75, 612-615. http://dx.doi.org/10.1097/00005053-193206000-00002
However, I tried reading it, the print is very faded and near-impossible to read.
How rare is it really?
1 in 125 million
From:
Daneshjou, K. et al. (2012). Congenital insensitivity to pain and anhydrosis (CIPA) syndrome; a report of 4 cases. Iranian Journal of Pediatrics, 22, 412–416.
But in this paper on the epidemiology in Japan, it's estimated at 1 in 600,000–950,000
From:
Haga, N., Kubota, M., & Miwa, Z. (2013). Epidemiology of hereditary sensory and autonomic neuropathy type IV and V in Japan. American Journal of Medical Genetics Part A, 161, 871-874.
Is it hereditary? Or just a sporadic fluke mutation?
It's hereditary:
Congenital insensitivity to pain with anhidrosis (CIPA), also known as hereditary sensory and autonomic neuropathy type IV (HSAN IV)
Kim, W., Guinot, A., Marleix, S., Chapuis, M., Fraisse, B., & Violas, P. (2013). Hereditary sensory and autonomic neuropathy type IV and orthopaedic complications. Orthopaedics & Traumatology: Surgery & Research, 99, 881-885.
So what is the life expectancy of someone with congenital-analgesia?
There's age distribution of the population in Japan:

It doesn't say life expectancy, but it seems that it won't be past 40 years.