system
Given the following post, respond as if you're commenting on Reddit:
human
[Dune] We're told over and over that the spice has "geriatric properties", but what does that actually mean?
gpt
Geriatric = an aged person.  So it lets you get older than normal

"Without melange and its amplification of the human immunogenic system, life expectancy for the very rich degenerated by a factor of at least four"    

It lets you get older by a lot.