Maggie's ears stand straight up and have since about 5 or 6 months of age (she's 3 now). However, Max is almost 6 months and has floppy ears. I really don't think they'll ever stand up as they are big, haha. In all honesty, I don't want them to. He is so stinkin' cute with them flopping over a little and I'm not showing him, so who cares? I love him however he turns out.
If your puppy ends up having a little flop to the ear, embrace it.. it gives him character.
There's no use in stressing over it.