Tortoise years

Griffin (8): How long is a tortoise year?

Me: Good question. Maybe six months?

G: Huh?…A tortoise lives 250 years and a person lives 75 years…I need to divide those.

Me: It’s about three.

G: A tortoise year is three years then.

Me: No. It’s the other way around.

G: Oh. Then it’s four months.

[Next day]

G: A dog year is . I’m not sure how many months that is.

Me: Is a dog year  of a year, or is it seven years?

G: Well a dog would age one year in  of a year, so it’s .

Now I don’t know what a dog year is!

The boy makes a good argument.