Does this still hold true for you if we extend your example to say, an 11 year old?
Why do you believe that puberty coincides with the stage of cognitive development and maturity necessary to understand the repercussions of sexual activity? Do you consider fertile pre-teens to be autonomous enough to make all other significant life choices for themselves as well?
An older adult having sex with a child of that age is an act almost certainly subject to (very) asymmetric information, deception and/or manipulation, and some degree of harm to the child occurring. It is therefore coercive, and should be judged as such.
I agree with Freedom, a lot of people simply don't like the idea of people having sex with someone much older than them, but this doesn't really make any sense, its just an aesthetic or moralistic preference.
What exactly do you mean by "asymmetric information, deception and/or manipulation?"
What makes you think this more likely to be done by older people? For instance, why is a 40 year old who is having sex with a 14 year old likely to be any more manipulative than an 17 year old doing the same thing?
How is this manipulation and deception you allege would occur any worse than the sort of manipulation and deception that occurs in relationships all the time? Is it the role of the government to stop people being manipulated or deceived in relationships?
If this is such a concern, should a similar age gap rule apply to people already over the age on consent under the current laws. For instance, should 16 year olds be prohibited from having sex with over 60 year olds?
Remember, the normal laws about sexual assault would apply, and these include protections for things like intoxication. So if the younger person is fully consenting, and we accept that they are old enough to meaningfully consent, why should we care how old the person they are consenting to have sex with is? We are just imposing our preferences on them and assuming young people don't really like to have sex with older people (this may even be true to most people), but certainly not for everyone.