Want to file OLD taxes. Please help.

Hello,
I made money with a hobby and odd jobs in 2010, 2011, 2012, and 2013. I was young and knew nothing about taxes. I only knew that I was making below the standard deduction amount and was told I was not required to file, so I didn't file.
Now looking back I wish I had filed. It's only 3-5K per year, but every little bit helps, right? 
Can I still file for those years even though I wouldn't have owed taxes? 
If so, how?? Where can I get those old forms and instructions?
Are there any downsides to filing now?
Thank you!!