In SR1 Core book, under the meta-species descriptions is where it's first mentioned, something like "genetic markers indicate a lifespan of..." (though I'm quoting from memory, at work, books at home). I've seen the same phrase/method used in my 4.5 month cramming of the last 5 years of SR 4th edition books...but I can't remember where, maybe Running Wild, Vice, or Corporate Guide (last 3 books I've read). 2nd edition but not 3rd (I think) mentioned the same thing in the species description sections. Both mentioned for the elves that all tests have been inconclusive (or something along those lines).
I could further belch out ideas like, "by using DNA markers, body mass, metabolism rates, etc., fairly accurate species lifespans can be determined with a minimal +/- 5% of median age. So for example, if tests indicate a median age of 75 years, we would be confident (3 sigma) that the natural age range of that species under optimal conditions and environment would be from 71.25 - 78.75 years." But I stress "belch."
