His fingers look especially nubby, though. Probably because they're squared off at the ends. Nothing says Astro Boy like massive, chubby hands and forearms, though... idk why; in the manga he was usually drawn fairly proportionately, if a little chunky in spots. Just a little bit. It got exaggerated in the 60's series, but it carried to all his limbs, not just the forearms. His upper arms were still pretty chunky, too. I remember Cobalt having forearms disproportionate to his upper arms... he was a gangly, awkward sort of thing, the poor creature...
He tried to draw Atom looking a bit older, to make him seem "cooler", at least in his own opinion. But most people liked him littler, and so Tezuka continued to draw him smaller and smaller, going past the point of where he started. After a point, Atom was just a chubby lil nub.

Come to think of it, the 2003 series had him with very chubby arms and limbs... maybe that's why I associate such features as belonging to him. He wasn't quite as exaggerated in the previous series, as I said (with the exception of the exaggerated and simplified 60's anime, and maybe parts of the manga, the smaller he got). This is also the series I remember from my own childhood, regardless of how little I likely actually saw or maybe even liked of the series. Also, in the 2003 series, he was actually taller than in previous generations, but still gave off the impression of being quite small and young. Maybe because everything about him was smooth and rounded (save his spikes, which even then were streamlined to be curved on one side into a taper at the tip)...
But yeah, depending, I can actually like an older-looking Atom. I like the "Atom Returns" arc version of him (which I think I may have initially been put off by him, for the same reason I think I kind of like him now: his eyebrows
