Depends on what you mean by "mountain" and "new". The Himalaya mountains, for example, are very young. read more
In truth, there are three ways in which mountains are formed, which correspond to the types of mountains in question. These are known as volcanic, fold and block mountains. All of these are the result of plate tectonics, where compressional forces, isostatic uplift and intrusion of igneous matter forces surface rock upward, creating a landform higher than the surrounding features. read more