Yeah, it's like if you have a kid in 2020, who has a kid in 2040, who has a kid in 2060... But of course it depends on what age people have children at. 25 is more like for modern industrialized societies than less developed agricultural ones, but who knows.
In a time or place where women are pregnant every other year from 15 to 45, the average generation is 30 years.
In an average industry nation with two childs at 22 and 28, the generations are 25 years.
In societies where men can have several women and/or are usually much older than their wifes, the average generation can easily go up to 35-40 years.