[Rush17]

When an Ace completes it on 3rd, get raised by a low card, and then check/calls a turn bet after what appears to be a brick...(unless he's a poor, eratic type player)he probably has a pair (whether it's Aces or not is hard to tell at this point because some players go into check/call mode if they brick and their opponent does not; mostly as to disguise the strength and to possibly position themselves to CR the later rounds. And if he doesn't have a pair, then he must have started with a wheel draw and feels that a peel is justified due to pot size. Again, this is presuming that he's a thinking player.

That said, I think you need to bet 5th. If the Ace door does have A's, then he's going to call you anyway, but it's doubtful that he'll bet if checked to seeing that he had his chance on ~3rd-4th and chose not to bloat the pot. And if he picked up his low draw, then he's obviously going to call but there's nothing to make me believe that he'd bet if you checked it. The pot is getting pretty big and why give the low draw a free card.

And, going by the looks of the other player's board, I highly doubt that he's going to bet either, but, if he called all the bets/raises thus far, I think it's very likely that he's going to keep calling. So why not bet? Besides, because it's hi-lo and not stud high, a lot of players are going to put you on a strong low draw who just paired up on 5th anyway.