Life coaching is a non-regulated industry, so there is no license or degree required. There exists no official accrediting institution or governing body in the life coaching industry. There may be organizations that claim to be an official or legal accrediting body, however this is false. Therefore, anyone can coach based on their own level of comfort with their chosen training and/or past relevant experience. As long as you are not going outside the scope of coaching, such as practicing therapy (for mental health, for instance) you are free to coach as you wish! It is recommended that any coach who is concerned regarding this matter seek advice from his/her state.
Most life coaches do not have any official experience in a field that is directly related to life coaching. Instead, they bring with them both their life experience and their unique work experience. Often coaches coach in a specific niche, in-which they have unique knowledge and experience. For example, entrepreneurs coach business start-ups, personal trainers become health coaches, teachers coach others on public speaking, etc. In most cases, coaches enroll in training programs before beginning their coaching practice. This gives them a foundation of understand about what coaching is, the psychology behind it, and methodologies and processes used. There are a variety of programs out there. Some are basic, some advanced. Some are about coaching in general, while others focus on specific niches. Ultimately, what training you need in order to coach is up to you.