"Never discussed".
HA!
Humans forget a lot.
Kes doesn't.
(Kim remembers being born ...Shut up!)
You might remember 0 minutes to half an hour of any random day in your life, but she remembers every second of every day.
The collected memories in her brain of one week is more raw data than one of us might keep from a life time.
Of course %99 of that data is absolutely nothing of value.
Have you ever heard the reverse argument for Vulcans?
That because of their life expectancy, they mature slower.
That they shouldn't be looking for a teenage sexual dalliance till their 40s.
(But it's really easy to find evidence to blow that theory out of the water.)
Does she ever refer to her captivity by the Kazon even in passing? You'd think she'd be deeply traumatized and would despise the Kazons for what they did to her. Do you think its evolutionarily possible for there to be a sentient species w a "normal" lifespan of only 9 years?