If they are not supportive of the relationship you could find yourself being accused of wrongdoing, even though nothing has occurred. It is not unheard of that they then claim "rape." In addition, parents of those minors have some say in what activities they permit their child to participate in. What happens when you decide that you don't want to date that individual and they are angry, jealous of your new dates, etc. Otherwise, a dating relationship that does not involve any sexual activity can be "legal," but you can expose yourself being potentially accused of illegal behavior, to say nothing of the temptation that may lead to illegal behavior. It is still high if the adult is 3 or more years older than the minor.
That liability is very high is the minor is under the age of 14. Why do you need to have this explained to you? Which situation is it, or are you just generally curious and want to know? My advice as an attorney is that no adult should have a relationship with a minor, even a "dating one," as it opens them up to huge liability.