Loving history is a good start...and you've probably already got that down pat.

In a lot of ways, the study of history comes down to understanding the people of the past in their own context (NOT today's modern context). To do this, historians rely on what are called primary sources - accounts of events written at the time (usually by eyewitnesses). So, in military history, for example, one might rely on after-action reports and memoirs. So, building a library of primary sources of the history you are interested in is a good start (and, depending on the particular event, such as World War II, there often is no shortage).

Learning how to read them is a different skill - in a memoir, the further away from the events somebody is writing, the more likely errors have crept into their memory. There are also cases where somebody is attempting to rehabilitate their reputation, and their account is filled with misrememberings and sometimes outright falsehoods as they try to make themselves look better to posterity (this happens in many of the memoirs from key players in Nazi Germany after WW2, to take an example).

You will also want to build a library of secondary sources - books written about events that are not written by eyewitnesses. I would suggest moving from the general to the specific. So, if you're interested in WW2, for example, you might start with one volume histories of the war, and then read something about the Battle of the Atlantic, and then read a book about the British or Germans in the Battle of the Atlantic, and perhaps then read a book on Operation Drumbeat, which took place over several months in 1942, etc.

But also, take history classes in school, and try to get into a Master of Arts program where you can write a thesis. The training you receive on how to research and judge sources is invaluable, and you cannot complete a thesis requirement to a degree without having a working grasp on how to operate as a historian.

But, all that said, and this is the most important thing - have fun. History is a field for people who love it, and it is very easy to spoil your enjoyment by treating it as just a checklist of tasks to get through on your way to an MA or PhD. Read the stuff that interests you, and engage with it in ways that you enjoy (building models, writing stories, playing games, building up a library, etc.). And then, when you're an adult, if you still want to be a historian, you'll have a firm foundation to work upon.