Come second to the habits you have formed.
We all spend our 24 hours a day using our habits. To make a new one also requires breaking an old one. Even wasting time is a habit.
So when you want to start exercising. Or writing. Or any other habit, it starts with replacing the old one.
When we’re young the habits are what formed by external factors around us, as we mature, there is opportunity to see what you want your habits to be, and adopt them.