I am a super newbie to touring as well but one thing I've learned through years of fighting fires and a lot of hiking is "Find your pace". I can hike all day uphill at MY pace. Any faster and I peter out. Once you find your pace don't be intimidated to keep up with others, just keep your pace and roll on, you'll get there. In fact you'll probably pass many others who attempted to go beyond their pace. I have found that although fitness is big factor, personal pace will determine your stamina.