So I read this book that had a character the same age as my 7-year-old daughter. This character vacillated between doing things that my child would have done at the age of 3 and things my child probably won’t do until she is 14. And you know what? This drove me nuts. I know I am a trees person and I get my knickers in a knot over details many people probably wouldn’t see, but this one in particular drives me crazy. If you want to write about characters of a certain age, you HAVE to have a beta reader who is or knows that age. So, if you are 40 and you’re writing about 14-year-olds, yes you need to get betas of that age (or, at the very least, betas who are parents or teachers of kids that age) and if you are 14 and you are writing about 40-year-olds, you also need to do the same thing. Don’t assume you know how a 6-year-old acts if you’ve never been around one (it does not count if you were one 20 years ago!) and don’t assume that you understand the motivation of a parent if you haven’t been one either.
I’ve said it before but I will say it again: making mistakes like this weakens the strength of your narrator and thus of you, the author and once you lose that trust, you can’t get it back.