I've decided that it can't be mapped to human ages, and I'll explain why.
I started out with a couple, and at the beginning of the YA stage (20 ish) they adopt a child (at the beginning so 7 ish). Many days later they are aging up to adults (40 ish because if it was 30 YA and A wouldn't be the same length) and the kid is still middle of teen (16 ish)
The difference between 20 and 7 is 13 and between 40 and 16 is 24. It doesn't work. I just refer to how many days old they are now.
(This is on normal lifespan)