I suspect most people younger than eighteen would have a really hard time understanding philosophy. First, there are a number of prerequisites. You might have a hard time understanding philosophy if you haven't taken any science classes (including the social sciences), for example.
Second, I think life experience is VERY important.
I was forty years old before I opened my eyes to politics. I quickly became a student of political science and a political activist. But it was another two decades before I began studying philosophy.
Of course, I'm just an anecdotal example, but, based on my observations, I have a hard time understanding how anyone who hasn't graduated from school and explored "the real world" could understand politics. They might understand certain facets of politics, but I don't think many people are going to grasp the big picture without that vital experience as a worker, teacher or victim of the state.
Ditto for philosophy. On the other hand, if you have an interest in philosophy even before jumping into the real world, fantastic. You'll have a head start over many people.
Just remember to keep an open mind, because it's a roller coaster ride. I'm still revising my views on various issues.
Another interesting thought...
I still haven't read a great number of philosophical works, so I'm not sure how accurate this is, but it seems like most philosophical works are epic, anal retentive exercises in arrogance. One could easily get the impression that the authors DON'T WANT people to understand what they're talking about.
It would be SO helpful if the authors would include more subheadings, bulleted lists, tables and simple pictures that illustrate the main text. A nice summary at the end would be nice, too.
The same is true of political texts.
Keep in mind that we're living in an age of rampant propaganda, and many philosophical/political texts are likely confusing by design. In summary, it isn't enough to understand the book you're reading; you should do some research on the author and try to figure out if his or her book is even worth reading.