Let's get wild now or never. A more literal translation would be: If we still don't try to do something crazy now, we would be too old (to do it again). Other examples: 再不起床你就要迟到了。 If you still don't get up , you are gonna be late.

再不疯狂means it’s time for you did something crazy,you should have done something crazy earlier,but you didn’t. 再here means “the deadline of your doing something”, “the last chance of your doing something”,this word is used here to emphasis the ‘desperate’ for you to do something: Never wait any more!Do it RIGHT NOW! Otherwise there will be some serious consequences happening.（like getting old，being late…，die） other examples： 再不起床你就晚了（If you don’t get up RIGHT NOW, you definitely will be late.) 再不救他，他就会死的(If you don’t save him immediately,he die.) 再不起床=不马上起床 再不救他=不立刻救他 So 再here can be translated as “right now”or”immediately”

The 再 here means "again" or "to continue". This implies that you had done this before and so a repeat now. The translation should be, "If we don't continue/again to act crazy, then we will become old"

“再”的意思是：对于“不疯狂”的状态的持续下去

if you never try it.do it，the thing you wanna do it or u shoulda do it，even now，the last opportunity，you will find there will has a old man who inlay pearls on his face.He musta be regret that he doesn't have courage to try it.And he will be a lame child.So the word “再”in this sentence “再不疯狂我们就老了”，it means “if”.ye，Chinese is a complicate language，for example：我想过过过儿过过的生活。我想过/过过儿/过过的生活，我想过过/过儿/过过的生活。they have different meaning.each word “过”also has different meaning.but the key of life is keep learning the new thing.so go head，Sam N Cason，hah.