Unfortunately, that was a factor I overlooked when I was 10 and had a chance to speak to Leonard Nimoy at a 1973 auto show. I worked out this relative aging process that made me reason Spock was something like 70+ years old during the 5 year mission. I never stopped to consider Amanda was nowhere near 90 years in "Journey to Babel". D'oh!
Looking at what has been achieved in recent years as regards gerontology, cosmetic surgery, etc. maybe Amanda really was a lot older than she looked.
Don't think it was something any of the series ever went close to. Mention of Human lifespan (as compared to Vulcan) was never made, and the inference seemed to be that Humans more or less aged at the same rate as now (best reference seems to be TOS's 'The Deadly Years')