In TWOK when Dalinar fought with the knight radiant, the lady knight said Harkaylain was not often wrong in anticipating desolations. Which means Harkaylain must have fought several desolations. I'm thinking the time between desolations couldn't be just for a couple of years or even decades or else humanity would have been wiped out if they came so frequently even with the radiants. Leading to the conclusion that surgebinding must affect how radiants age if Harkaylain has a track record on knowing when desolations come.
Of course this hinges on the Heralds not breaking so easily and that the desolations are so destructive that there must be time for humanity to recover. Also Dalinar did not really describe Harkaylain in a way to determine his age so its just speculation.
Anyway I was thinking about this because Jasnah will be in her late 40s, early 50s in the second half of the series. Brandon would be doing something different if Jasnah is actually that age but I'll go with surgebinding slowing the ageing process.