I agree, I would have folded this hand preflop, especially against the button's sizing. Was 7x standard opening raise size in this game?
To your original question: Why do you think you are ahead of his range with an unimproved ace, a monotone KQ9 board, and an all-in shove against a large preflop raise?
Even if he was playing loose, that would mean he has a lot of hands in his range and there is more possibility he could have connected with the flop. Shoving all-in to a preflop raiser is further indication he is stronger than you think. For a quick run-through, lets look at a sampling of hands could be beating you. Flopped flush, straight (JT), sets, two pair, AA, JJ, TT, 88-22, AK, AQ, KJ, QJ, J9, T9, and these are just the reasonable hands. Throw in some other possibilities if he is playing really loose (like 95s) and you can see there are a lot of combos. Now, some of the combos we assume he would raise or three-bet preflop, but it doesn't reduce the possibility down enough, especially with the shove on the flop. I think the real icing on the cake is the fact he could have AJ, a hand that missed the flop, like you, but is still ahead of you. All of these combos coupled with the action suggest folding to his shove.