Bluff bet this river?

[chesspain]

Foxwoods 5-10 kill game. MP is a non-tricky, passive, elderly Asian man. He's too loose preflop and on the flop, but will rarely call down with a hopeless hand. Button is a quiet guy in his late twenties, trying to play well. They both should realize that I'm a TAG. I won a decent pot last hand, so I'm posting a $10 kill blind in LMP, with the hand playing as 10-20.

Preflop: chesspain is LMP with Q [img]/images/graemlins/diamond.gif[/img] J [img]/images/graemlins/club.gif[/img].
Two early players call, a couple of folds, passive, old Asian dude calls, I check my blind, folded to Button who raises, blinds fold, everyone calls. (10 SB)

Flop: A [img]/images/graemlins/spade.gif[/img] K [img]/images/graemlins/club.gif[/img] 7 [img]/images/graemlins/heart.gif[/img] (5 players)
Checked to Button who bets, both early players fold, old man calls, I call. (13 SB)

Turn: 4 [img]/images/graemlins/club.gif[/img] (3 players)
Everyone checks. (6.5 BB)

River: K [img]/images/graemlins/diamond.gif[/img]
Old man checks...

Since I assume that the old man would have bet this river if he had a king (although he could have a weak ace), and it now looks as if the Button doesn't have an ace, can I steal this pot at least 15% of the time with a bet here?