Kohlbergs stages are not defined by ages. There are often ranges given, and those given here were off from what is typical. The 300 page doc (p. 221) says the ages that people go though each stage are:
Preschool
Older children (Jr High/Highschool)
Adults
Other sources I've seen are simular.
https://opentextbooks.concordia.ca/lifespandevelopment/chapter/5-12-kohlbergs-stages-of-moral-development/
https://socialsci.libretexts.org/Bookshelves/Psychology/Developmental_Psychology/Lifespan_Development_-_A_Psychological_Perspective_2e_(Lally_and_Valentine-French)/05%3A_Middle_and_Late_Childhood/5.12%3A_Kohlbergs_Stages_of_Moral_Development
Some even say that few adults make it to post conventional. The original ages were quite off. And to even say ages, as people can stop in any stage, is slightly contrary to the idea, but large ranges that are typical are normally given.