Same problem here, the only difference being that I'm planning a little more crazy, over-scaled route for my first trip, being a 17-year-old travelling with only a friend at the same age. That is to say, from the cold north up here to Berlin - Paris - London - Amsterdam - Copenhagen and then home to Oslo and Tønsberg again.
What do you think? To ambitious? :P
I mean it seriously, it would be fun... just to show my parents that I can, experience some train travelling (I've taken the local train a coupe of km twice, that's it) and to experience a whole lotta Europe in one turn. :P
I also do wonder if it is any downsides at all being under 18.