@SaiyaJedi:
It's perhaps more noticeable now because his drawing style has grown "looser", such that the characters are drawn more to fit the needs of the scene rather than a set "reference model".
Excellent point!
Looking back, there's a lot of variance in appearance from frame to frame. Small details like the size of a chin or the angle of a jawline or hairline can make a huge difference in how we see a character, as well as how "old" that character appears to be. These little things can also make a character's face seem "off", even though it's hard to place exactly why it feels "off".
For example, when I first read the "Crewmember Zoro" (485) chapter, the face-forward images of Zoro (page 12 and page 19) felt "off" in comparison to the left-profile pictures (page 6 and 14) – but I couldn't figure out why they felt "off" -- it was just a vague feeling of "not-rightness" -- though the feeling of "offness" didn't detract from my enjoyment of the chapter.
Thanks to your insight, I see why now why those images felt "off" to me -- if I compare the face-forward images to the left profile images, I see that in the face-forward images, Zoro's chin is smaller, his mouth is less "anchored" to his face, his nose is smaller, his hairline is receding at a different angle (there's more hair than usual at the top, too) and his ears are larger and placed differently on his face. Also, on page 19, his face is so soft at the chin that it's almost circular! These attributes, though they're more like Zoro than, say, like Luffy, are on the border of what constitutes "Zoro-ness" so that's probably why they felt "off" to me, and while the left-profile images didn't. The left-profile images are more consistent with the range of attributes that we think of when we think of "Zoro".
It works with age too: on page 10 -- with his smaller ear, softer jawline and fuller hair style -- Zoro looks like he could be 20. In the left-profile image of him on page 14 -- with thinner hair, receding hairline, stronger browline and jawline, and bonier forehead -- he looks more like he's 40. But even though his "age" is not consistent visually in this chapter, it's consistent with the theme of the chapter: he looks most like a 20 year old when he's behaving like a 20 year old, and most like a 40 year old when he's behaving like a 40 year old.
Speaking of age changes, with his small head, softened facial features and tiny nose, Luffy looks like he's only 10 years old on page 11. Compare it to an indential pose on page 4 of the previous chapter, where his less-round head, slightly larger chin, bigger muscles and not-as-soft expression make him look more like his proper age. (But since chapter 485 is all about saving Luffy when he's in no condition to save himself, it suits the chapter to have Luffy look so young and vulnerable).
Disclaimer: all observations were made on scans of varying quality
Disclaimer 2: it's 4:30 am .... .... (my insomnia is talking).