Not clear what or who the subject of these sentences is My translation:

当你长大，你慢慢学会几件事情；有些人不必理会，无论他说什么做什么，多么幼稚又多么讨厌，真的不需要在乎。有些人永远成不了你的敌人，不必抬举他，这种人太看得起自己了，以为拼命攻击你伤害你，就能够被你所恨。有些人不必等待，你心里其实清楚得很，这个人不必再等了，只是你放不下.
As you grow up, you slowly learn a few things; there are people that (you) don't need to understand/care about, no matter what they say or do, regardless of how naive or annoying he is, don't pay any mind/depend on. There are people that will never become your enemy, don't praise him, this type of person cares too much about himself, will go all out to hurt you, will be hated by you. There are people that (you) don't need to wait on, actually inside you are very clear, don't wait on this person any longer, it's you that can't let go.   

How is my translation? Would appreciate your corrections. There are many I dont really understand:


有些人不必理会. Actually there are two translations I thought of:
A.there are people that just don't understand (dont understand what? "You"?). 
B. There are people that YOU don't need to understand/care about.
Which one is correct?
有些人永远成不了你的敌人，不必抬举他，这种人太看得起自己了，以为拼命攻击你伤害你，就能够被你所恨。this sentence is talking about someone that can NOT be your enemy, yet this person is doing his worse to hurt "you" and "you" will totally hate him? Is there a double meaning to 敌人 that I don't understand?


Thank you very much
有些人[你]不必理会. 你 is dropped as the context is clear. If you read the sentence again, it starts with:


  当你长大，你慢慢学会几件事情；有些人不必理会...


Chinese is a pro-drop language, you will encounter this quite often. 理会 here does not mean understand, but to bother or care about. So, it is saying, there are some people that you don't need to care about.




  有些人永远成不了你的敌人，[你]不必抬举他，这种人太看得起自己了，以为拼命攻击你伤害你，就能够被你所恨。


Some people will never become your enemy; there is no need to flatter them. This kind of person thinks too highly of himself and assumes that by attacking and harming you relentlessly, he will be hated by you.

There is no double meaning here for 敌人. It is just a philosophical statement advising you not to bear grudge against an unworthy opponent.