If an amine wants me to accept a character as a minor they should have them act like minors. In the same way I don't accept the bullshit of "it's okay she's 1000 years old guys" I don't accept the bullshit of "it's not okay they're actually teenagers guys"
If a character looks, acts and is treated like an adult, in my interpretation of the story, they're an adult. Cannon be damned
One piece is based for having the main characters be like, 19 at youngest iirc. So many shows (like JoJo) will have dudes at 6 foot 5 and muscly as shit and women who look easily in their 20s and go "theyre 15 tho".
Say what you will about Odas weird art style, at least his characters look their age and he isn't making weird sexualized teenagers.
Luffy starts out at 17, but is 19 after the time skip. The youngest is actually Chopper, who is 15 at the time he joins the crew. But he's an anthropomorphic reindeer, so he gets a pass.
What works really well is that the characters actually do look and act their age for the most part.
