My guess at the not-too-distant future: a comedy-drama on HBO or some such where 45-year old Joe Schmoe is drawn reluctantly but irresistably into a relationship with Britney Bright, a smart, mature 13-year old girl. After a few furtive meetings the two decide to make their love public. After a period of ostracism, their obvious love is clear to all, and in a touching scene, Joe Schmoe is embraced by Britney's parents, Bob and Bonnie (who are younger than Joe). The happy couple is welcomed into normal society, where their age and culture differences generate madcap hilarity.
And the youngER girl/oldER guy plot line goes back to biblical times. Not exactly new.
While I find the idea of "child sex" abhorent, there's an effort on the part of many to paint the "child" label on sexually-sentient biologically-adult adolescents, and I'm sorry, but it just doesn't fly. According to the CDC, today's 13 year-old girl in this country is almost two years PAST menarche and as biologically functional as an adult. She has probably reached 95% of her adult height and has reached about 90% of her adult figure development. By the age of 16, those figures are closer to 100%. Yet, the American society wants to call these gals "children." Sorry, but that is counter to nature. Yes, these girls may lack the mental and psychological maturity to make what we oldsters would like to think are responsible decisions about their bodies, but that, too, is a fact of nature.
I'm not sure exactly when the artificial and arbitrary age of 18 was decided upon as the demarcation point between "childhood" and "adulthood," but I can tell you that "childhood" ends with the onset of puberty. Modern society enforces a sort of adolescent purgatory on those who emerge from childhood into self-awareness, asking them to function, in some ways at least, as children until they reach the chronological age of 18.0000000 years. Then, somehow, magically, they're no longer "churldrin."
Sorry, but that doesn't wash with me. You want to talk adult-child sex - i.e., with real "children"? Yes, it's abhorent and against nature and God. But once the flowers of biological adulthood bloom, adult-like behavior is instinctively driven to follow, and all the social strictures you wish to put in place won't stop it. It's happened forever, and will continue to do so.
As for your HBO movie idea - the real oddity these days is a 13-year old who is NOT sexually self-aware and developed. If you don't realize this, then you must lead a sheltered life, because it ain't th' same as when YOU went to Jr. High.
And your protagonist need not be "well-stacked," despite the contention by some here on FR that ALL adult women (by definition) have huge breasts, and if some gal does NOT, then she must be underage. No, the sexual organ that's most important in making the plot work is her MIND. You can see desire in the EYES, in the tone of voice and cadence of breathing. Big tits would spoil the illusion.
Michael