I know that Kled been around for a very long time, what I'm trying to do is calculate Yordle age to Human years, since the OP wants to know what Human age are they compared to, You're being to technical on something lore readers already know.
Lets get simpler, what age do you think Kled is in Human years(Centuries isn't Human years), because if we was that technical this what our age will look like:
26 years 4 months 18 days
or 316 months 18 days
or 1376 weeks 6 days
or 9,638 days
or 231,312 hours
or 13,878,720 minutes
or 832,723,200 seconds
See what I mean?
We're not talking about "Yordle Charm" because in Tristana's story it says the Bandits saw her as an "Old Lady" which she is not(She's Probably 18 in Human years) but because of her "Yordle Charm" that is what they see.