@Rogues':
Because it's one of Vegapunk's quirks? Who said that all Pacifista have to be identical, either in shape, gender, or stature? Like ice cream, Pacifistas can be built/designed in different varieties based on what's necessary for a particular assignment and what's not. Bulky, heavy, low-intelligence Pacifistas for combat that rely primarily on built-in machine capabilities (like the laser beams) and smaller, lighter, high-intelligence Pacifistas for infiltration/assassination that rely primarily on Devil-fruit based capabilities. That and to an adult, children appear less threatening by nature.
because I feel that the current reason for Sugar having stopped aging is a convenient plot contrivance on Oda's part. The literal ability of the fruit is to halt your aging from the moment you eat it. What would happen if a 50 year old man were to eat the fruit instead? His aging would be halted at 50 with the same toy ability. That's why I believed that having the devil fruit permanently revert you back to the age of a child regardless of what age you were when you initially consumed it would instead have been a much better reasoning than Sugar conveniently eating the fruit when she was a child and it conveniently halting her age from there. My Pacifista theory is another possible alternative to that.
Still the problem is that should Doffy somehow know about Hobi Hobi No Mi's effects, he'd also know that they don't halt aging at all. I know that not all devil fruits are cataloged but why take the risk he'd somehow know? It would be much more sensible to make her at least twenty years old so she could keep her cover for ten or twenty years forwards.
See first response above.
That doesn't explain anything. If Vegapunk already knew how to make cyborgs, then how on earth would it take ten years for a genius like him to make soldiers out of them?
She doesn't get along with her bodyguard. she repeatedly tells him to kill himself. She obviously finds him disgusting but only puts up with him because she requires additional protection as she's not as heavy artillery-packed as regular pacifista?
And why to give her ability to have such emotions in the first place? It's not useful for her mission whatsoever. Having bad vibes with your bodyguard doesn't help you at all.
Because cyborgs/robots are capable of eating food too? And having favorite foods just like Franky with his burgers and cola?
Franky is originally human. He has his own free will and personality. Sugar, if she was a pacifista, shouldn't have any personality quirks that would make her seem troublesome in Doffy's eyes, such as enormous consumption of grapes. They cost money you know. Or is Vegapunk planning to drain all Doffy's finances to grapes?
And most importantly, why would Vegapunk even give such a powerful ability in Doflamingo's hands? For what we know, Vegapunk is supposed to be really compassionate guy. Not someone who would give a power to erase people from other's memories and enslaving them to megalomaniac like Doffy.
Look, I'm trying to be as polite as possible but this theory… it isn't very good. Sorry man but it just isn't!