When people ask an Author, "When did you start writing?" or "How did you come up with that idea?", it's a great opportunity for the Author to open up and share his/her part of the journey in becoming an Author.
If you have a desire to become Author, it is critical you write what you know about most of the time. If you do, then your Boss (the Reader) will "experience" your novel, instead of simply just reading it and putting it down when they are finished with it.
When the Reader has a moving experience with a great book, all or parts of that novel stays with them for their lifetime: they think about it, compare it to other great books they love, refer to it, tell people about it and find a common bond with it in some capacity.
So, if you are familiar with the world of Medicine or the lifestyle of an M.D. that would be a great Hub to base your main character(s). If you have a law degree - maybe your central character should be an attorney?
I happen to be a football coach and it was comfortable for me to build the "Kenny Brown Mystery" series around a Collegiate football coach - even though there is very little actual football in my novels. Instead, in The Double Move and The Game Breaker, the Hero is caught in a very suspenseful situation and he must act upon his instincts accordingly to try and save his life and the lives of others.
Before you begin to write - find your comfort zone and choose a perspective you feel good about.
Once you do that - it makes it easier to build a story that intrigues your readers, and then everybody wins.
Be willing to accept professional critique from established Authors, it will save you time and effort, and you will develop into a more polished writer.
Author of suspense...
The Double Move
The Game Breaker