sure. you can still show them if the rest of the conformation is good. there's plenty of champions that don't have the 'best' rosed ears, but they have great conformation otherwise.
you can start showing as early as 6 months old. the best thing to do, if you want to show, is to just try it. see what happens. talk to other people there that are showing or having their dog shown. once you find someone that you are able to talk with (some are snobs, some are waaaay competitive, and some are normal, helpful people that love the breed and showing) then you could ask their thoughts on your dogs ears.
i'll tell you that most of the eb's with the perfectly rosed ears had their ears glued at least once, if not MANY times as pups.