There is a lot of great advice being offered here and I think you are doing an excellent job in listening to what everyone has to say and taking their advice into consideration.
I received my first horse on my 15th birthday and even though I thought I knew what I was getting myself into, I certainly did not. Like you, my parents did not understand horses and lacked horse knowledge. We basically learned as we went along and relied on the advice of horse friends and the barn owner. I had taken lessons and been around horses for quite some time prior, but owning one and working with/around one is completely different. I worked two jobs and worked at the barn to pay-off the board. It was a lot of hard work and many long hours. Not to mention at 16, I got my drivers license and started driving. At that age, you have high school activities come up and if you choose to attend college later, that too will require your time.
I love my first horse and I am very grateful that I was able to keep her through all of those life changes. However, the time and money I (as well as my parents) invested in being able to doing so was far more than what I had ever anticipated. Think long and hard before making this decision because you are at a very pivotal point in your young life