CLOTHES
You may be a hoarder if you refuse to give away a shirt that you've never worn and have had for years. It sits in your closet or a drawer untouched until the moment you're rummaging around looking for an outfit one night. You see it, remember that you've never worn it, think about wearing it, and then throw it back where it has resided for months. It probably isn't even in style anymore, but yet you still feel like there will be a chance to wear it.
T-SHIRTS
Now this also goes along with clothes, but I thought it deserved its own category due to its worldwide addiction. You may be a hoarder if you still have a t-shirt from junior high in your collection of shirts. Even if its only use is to remember an event, it still shouldn't be among your current shirts. Give it to your mom or grandmother to make a quilt that you can actually use because we all know you wouldn't be caught dead in a junior high shirt on a college campus or out in the real world.
PAPERS
PAPERS. School papers, receipts, info packets, you name it. If you keep unnecessary papers that will NEVER be of use to you then you may be a hoarder. For instance, it's the end of the school year and you're going through your backpack. Forgotten papers cover the bottom of your bag. Binders are packed with worksheets and loose papers. You look to see if you need to save anything for a future class or just to have handy. Everything you come across seems to be important and before you know if you have saved 97% of the papers that were once in your backpack. How did this happen? If you think that for some reason you will need it in the future (but deep down you know you won't) then you may be a hoarder. If you want to keep a paper as some "souvenir" from that time in your life, then you may be a hoarder. Anyone else would just toss that scrunched up paper to the side, but not you. For some reason, you think it will be of use to you later in life.
TEXTS
Let's be honest, we've all been there. You're running out of storage on your phone and you're stressing because you need all the room possible for future pictures. You may be a hoarder, even just of the text variety if you refuse to delete conversations with people from months before. I'll be honest, I absolutely love having old texts from people to look back on. I can never bring myself to delete texts from my close friends because they hold so many memories in them. My inbox holds thousands of texts that I know I will never delete. If you refuse to give up on technological writing, then you may be a hoarder.
CLUTTER
If every surface in your room is covered with a knick-knack, picture frame, or old bottle of perfume, then you may be a hoarder. You may even get in an extreme cleaning mood and organize your heart out, yet it still seems as though you've done nothing. Trying to find a place for everything in your room is a struggle and it gets messy after one morning of getting ready. When you buy something new, you never get rid of something else from your room so the collection keeps growing.
I'll end with a word of advice: don't wait until it's too late to get rid of unnecessary things. It will become all too much when you have to move your belongings from one to place to another, trust me.