Do あなた think Killer is Sabo?

No, killer is 25 before time skip.. Sabo would've been 19

I somehow doubt it. Killer could be Sabo, but since he, much like Ace and Luffy, had an interest in leading a crew and not 芝居 as 秒 in command, it just seems unlikely. And before anyone says it, yes, Ace was not captain of his crew in the end, but we're talking about the difference between one of the Yonkou and a Supernova. Pretty huge one there. Beyond that, Sabo is unlikely to 登録する a crew that's just out there to do as much damage as possible. Pretty much the only reason he might be Sabo is that he's generally the right age and has blonde hair.

SPOILER!!!!!!

Sabo isn't killer. It's pretty much revealed in マンガ chapter 731 that Sabo is alive but when he appears killer is on some other island in the new world.