Is depression something you're born with or something that is gained over time?

Depression is definitely not something to be born with! You can't possibly be born with a feeling like this. 

It's gained over time, and also depends on the environment you're in. 

- Being depressed is caused by outside things. Things that are happening in your environment, or around you, that  make you feel that way. 

If you don't have the need to be depressed, you won't. 

It all depends on the control you have over your emotions and feelings. 

Depression can most likely stay for not that long of a time. Unless you've developed a disorder such as bipolar disorder, then the case differs. 

Hope I helped! Have a happy day! Don't forget to smile, because a smile can change someone's day! :-)