Inconsistent and unpredictable parenting is a common factor in children with oppositional defiant disorder and treatment often includes working with the parents as much as working with the child.
Since the focus of the article is on child development, it's reasonable that it limits its scope to parents of young children, and not e.g. parents of 50-year olds, even if building trust might be nice there too.
The title of the post we're both commenting on, which reads: "Why young parents should focus on building trust with their kids". I was assuming that the title was oddly editorialized, but it's also not that uncommon for articles to change their titles too so it's possible that posting guidelines were followed and it was the article itself that specified "young parents" at some point. Considering the age of the article though, I kind of doubt it.