If you are still looking for info about coaching certification, you might find that checking with International Coaches Federation useful.
I've been a coach for 15 years now and offer a Life Transition Coach certification program. In my experience, success as a coach is less about your credentials and much more about your willingness to market yourself and your ability to produce results with clients in whatever field you elect.
I don't bill myself as an Executive Coach because I have left the corporate world behind me. However, many of my Life Transition clients are executives who are discovering that their life is a mess because they've focused on their professional needs at the expense of their personal ones. Because I have a strong corporate background I can usually help them move forward in a way that keeps the two integrated as they move into the future.
In my experience, by the way, if you are looking to get corporate gigs for your coaching, having both an Executive Coach and Life Coach line of business doesn't help. Corporate folks are still pretty snobby and see life coaching as something for more junior people, not their senior executives! At least that's my experience.
Best of luck