I think it is. I occasionally got sad when I was a teen. I think my sister is melodramatic now. So it could very well be.
If you are permanently sad and feel a lack of motivation and joy in anything, you might be clinically depressed and should seek medical attention, although your description doesn't really fit. If you just think that this world is a rather dreary place to live on, welcome to the club of sane people.
Sometimes I think and invent sad stuff to feel sad and sometimes I feel and remember things that make me happy. I have a psychological need to feel things sometimes. people play scary games and watch scary movies for the same reasons. you are all normal.
It's very hard to get out of bad and do stuff if you feel depressed while getting up and doing stuff is actually the best way to fix it, Wich ironicaly seems depressing.
If you are clinically depressed this does not work; if this works (well, give it a try) you are not clinically depressed
Getting older doesn't seem super dull to me. Go to College, work your ass off, get married, have kids, die. But it's okay, I'm joining the military when I can, so that should throw some spice in my life.