The topic of younger protagonists in adult-themed manga is a complex one, and I tread carefully here. I've seen discussions in niche forums about certain works that blur lines, but ethical concerns always arise.
Most mainstream platforms heavily regulate such content, focusing instead on age-appropriate romance or fantasy themes. If someone's exploring this territory, I'd strongly recommend sticking to wholesome coming-of-age stories like 'Horimiya' or 'Ao Haru Ride,' which handle youth with far more respect and depth.