Welcome to Flyertalk, flame7926.
It depends heavily on your country of origin and your destination. Can I infer from your spelling of 'travelling' that you are based outside the US, for example?
From my point of view, I've been travelling alone (as in, not UM) internationally since the age of 13. From 16 onwards, my holidays were with friends abroad. Neither of these were a problem from a British citizen travelling within (Western and Eastern) Europe, although I never had the money for an actual hotel, and would end up in hostels, camping, or sleeping on trains instead, so that never came up. No documentation was needed for me to travel at that age (and the concept of notarised documents doesn't really apply where I live).
I suspect major hotels are more likely to be a problem, as they need a credit card for security, and may have insurance issues if you are under 18. If you don't fancy the hostel route, then smaller guesthouses may be a better approach.