Study Curve

I suggest contacting an international student travel organization. My guess is that you are now a student, and they will be able to assist with answers to many questions relevant to travel by younger travelers. They will be helpful with an international student ID card, student discounts, youth hostels, insurance, useful contacts; and of course, those legal/logistical questions.
Enjoy your travels!

It may also depend on where you are going. Different countries have different rules about travel and who they will let in. It is best to check out what ever country you would like to visit. The governments for most major countries have web sites that give you current information on these types of issues.

Here is what I found but I am not an expert.

If you are under 18 you must have consent from parents in writing and travel with someone that is at least 21 years old that will assume responsibility for you.

I should have been more specific, Can you travel 'alone' if you are under 18?

I personally have traveled internationally when I was 15 and I know many others who have as well. You just need to have your passport as far as I know.