Better to replace AOC with mental capacity test?

What about a legal framework that provides greater protection for children and adults without differentiating any group. By that I mean a legal model built on identifying harmful actions to other people and having strong laws to stop those actions but applying those strong protective laws to all people equally regardless of race, faith, age or any other differentiating factor.

So for example, assault, coercion, threats, physical punishment, pressuring someone to engage in a sexual activity through intimidation or deceipt etc should not be acceptable with legal protection covering such things. Age doesn't come into it, we define a set of standards that all people are entitled to. Everyone is entitled to respect, the right to say no, the right to choose who they love. As soon as we start to define boundaries such as gender, age, race etc we start to devalue whole groups of people next to other groups which I think should be avoided.

Of course children are different in the same way that adults with learning difficults are different in that they may not have the developed mental capacity to choose a partner or understand the implications of their actions. But the rules defined above can ensure protection without fixing an imaginary age line by having expectations such as someone can only give informed consent if they have a measurable developed mental capacity in relationships or they have consent from a guardian/parent and a health official.

When I say "measurable developed mental capacity in relationships" I mean that they should have a knowledge of relationships, what it means to be in a relationship and all the mental and physical aspects of a relationship. I mean how mentally developed someone is at doing maths or playing an instrument I'd suggest is or little importance. I can imagine a child could be highly developed at academic subjects but still be unable to make a good choice about a relationship but equally a child could be poor academically but be more developed at understanding relationships.

When I add the clause "or they have consent from a guardian/parent and a health official" I'm referring to whether people with less developed mental capacity should be denied relationships. Should an adult with learning difficults be denied the opportunity to marry or be with a partner? Should someone younger who's in love but perhaps can't pass a test? By requiring the consent of both the parents and a health practisioner it should ensure abuse doesn't happen and a person is interviewed and understands what a relationship is as well as ensuring responsible guardians and experts are aware of a relationship and there to offer advice and support. I'm not so sure about this point, perhaps it's better to just require a measurable level of mental understanding but that could deny many people, adults and children from being able to have relationships.

So here I'm proposing offering more protection to all people including those with learning disabilities. Who wouldn't want better protection?
I'm also proposing removing legal gaps by applying laws evenly to all people.
I'm also proposing that relationships no longer have to be hidden but could be open and get better support and protection.
I'm proposing measuring people by their mental capacity to have relationships, not a magic imaginary age line where we all become sexually capable at 16. Many people at 16 shouldn't be in a relationship while others at 12 or 13 could have healthy relationships.

What do you think? Is it safer for the law to just have a hard fixed age line. I can understand the benefits of that, it's easier to police so cheaper for the courts and whole legal system and everyone knows where they stand. But is the fact that it's easier to police more important than providing fairer and safer cover to those who need it? A 16 or 20 year old might not be that developed mentally and lack real protection. Meanwhile people are having underage sex secretly all over the country because high school kids are all hormones and have to be secretive. So would a mental capacity test allow people to get the support and protection they need and stop relationships being hidden?