That's more to do with their original role having extremely high mortality rates. "Honoured Elder" titles for those who live to 20 were exceedingly rare. DS9 only really mentioned them once when Dax spoke with a Jemhadar during the Iconian Gate mission, then later in the episode the runabout shrinks one of the invading Jemhadar was an Honoured Elder but still only Third or something. Without a life purely focused around combat the lifespan may end up far higher than expected.

It's still going to be done extremely poorly in this show, however.