That is an unfortunate case of what it looks like today maybe. A more approriate path to take would be to make it so that if both partners are close to eachother in age no such thing should apply.
To sum it up: legal with sex between partners close to eachother in age before age of consent is reached but I do not believe there to exist healthy relationships between someone who is 13 and someone who is 40-50 years old. They're in very different stages of life.
I fully support a 14 year old having sex with another 14 year old, it's part of that period in life. However, a 14 year old with a 40-50 year old? No.
Those same drugs will cause physical development problems which will create a generation of imbeciles.
I have no problem with children having sex. If they use protection, if they both consent, if they're both well educated. Children who will experiment will do so anyway.
The problem is that, when both participants are not of the same age category (before adulthood), you've got a severe disparity in power. And thát causes problems.
Your utopian vision might be great for reducing the amount of people on this planet, however. Hell; it'll toss in a few wars over candy that'll kill millions. Great idea!