Ace is already at sea when Kuma makes his deal, which means Luffy is at least 14 in that flashback when Bonnie is 8 or 9. I would guess it's 15 and 8 (since Ace is with Whitebeard already) when the deal is made. So 19 and 12 now.
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"Hope is allowed to be stupid, unwise, and naive." ~Sir Chris