In many places the law takes this into account by forbidding teachers from sleeping with their students, or bosses from sleeping with their employees of a certain age, even though somebody who is not the teacher or boss of the person can still legally sleep with them. If power difference is your main concern it would seem that this is a better solution than arbitrary age restrictions. There is a huge power differential between a billionaire adult male and a poor adult female, should we forbid them from sleeping together as well? The issue boils down entirely to consent, and if a 14 year old can consent to sleep with a 14 year old then a 14 year old can consent to sleep with a 30 year old.