Does adult cat food eaten by a kitten have any major ramifications for the kittens overall health?

We have a 20 month and a 5 month old cat living together, so we need to watch when theyre eating their wet food together, because the the kitten will try and eat the adults food, which we stop. Im mainly asking because a friend who also has had cats for years, from kittens, has only ever fed them adult food and theyve grown up fine.