Max's ears didn't stand up until he was around 13 or 14 weeks. I'm not sure exactly when but his pictures at 11 weeks have floppy ears and his pictures at 15 weeks have ears that stand up.
For several weeks he had one ear that stood up and the other flopped over. I have read that when they're teething a lot of times their ears will fall.
This picture is of Max at 11 weeks old.