I don't have any supporting evidence other than he's probably not a shicibukai because why woulld they want someone so old they should have some fresh muscle man.
He has an operating sword that still has kuma blood on it, mmhm.
And he planted supa hi-tech hole mines under the bar gamble thingy.
On another note how did Hancock beat up alll those pacifista at marineford... I mean robots don't have feelings...do they?