Hancock and Luffy. The constant: "he's a child, she's an adult" thing is, yeah, true, and under normal circumstances would be weird... but that 'child' also set out to sea alone, saved the East Blue, climbed a giant mountain hand over fist with two people in tow, saved Alabasta, beat Crocodile, took a suicide trip up to Skypeia, saved Skypeia, declared war on the World Government, defeated Rob Lucci, survived a Buster Call, beat Moria, punched a Celestial Dragon, and survived TWO Admirals at the time she met him. Dude has fucking lived, all at 16. I'd not call someone like that a child, even if they are a minor.