So, I have had a friend go through this, it's just a stage, where you like rebellion, and the fire and darkness it your feelings and represents your inner self. You can meditate a lot and really focus on calming your 'inner beast'. What helps is watching your tempers and writing a 'dark journal' as I call it, that focuses on the darkness of your heart and thoughts. Preferably a locked one, then writing a 'light journal' that focuses on you light or qualities that relate to your element and happiness. It will help centre yourself, so you can focus on your true powers and potentials. Every year do a cleansing ceremony (of your choice) on anything and everything and burn the old journal with a ritual that you can write or, if you want I can email you one. The ritual will basically banish all the negative thoughts and bad things in that book, helping to erase them, keep your light book safe and more powerful.
A lot of people believe in five elements,fire,air,earth,water and spirit,when i think about it that way,i like to think of light and darkness as being part of spirit,so in that way,yes it is an element,i also think that some other people think so,but in a different way,i'm sorry if the way i put that sounds silly or childish.
The traditional elements are Earth, Air, Fire, Water and Spirit. Light and dark lend from aspects of Yin and Yang or masculin or feminin. Different polarites. Each of these has a different energy so you have to just relax and listen to your inner feelings. If you feel drawn to Fire then that may be one of your elements.
In my belief the pentagram has five-points the top is akasha which means spirit next is air next fire next earth next water it can be in any order really but for me akasha has to be on top your zodiac sign has nothing to do with your element and yes to a previous post it is very rebellious I would say you are 16-18 blessed be!
Aquarius is your SOLAR sign,but everybody also has a LUNAR sign,if you feel that way then you might be closer to your lunar sign,my solar sign is sagatarius,but i feel closer to water then fire and my moon sign is aquarius,this website can help you find your lunar sign http://www.lunarium.co.uk/moonsign/calculator.jsp .
Even then , there are more than a lunar sign , there are signs for the planets too , so a person signs would consist of a Sun sign , moon sign , mars sign , Venus sign etc and henceforth
By simply meditating on it and then judging which one you are closest too . The most balanced of individuals and the most ideal states is to be close to all the elements so one may not find one that you are closest too through meditation as one can be close to all
And Darkness is not an element . Yes , in a way , it is a very "real" thing but it is not an element . It came to being by interactions with the traditional original elements.