You can fall in love when you are 13, no doubt.
Love changes over time though. When I was 13, I was with the "love of my life"! However, now I can say he was my first love, and we'll always be friends, but I'm SO glad I didn't marry him ;)
Since you're so young, you just have to let the love grow and morph into whatever it will be. It could last, but it may not.. time changes people. Now's the age to have fun :)