Turning 40 can feel like a monumental time in a person's life. You might assess what you've achieved so far, how happy you are with your choices, and then -- decide it's time to make a career change. Changing careers in your early midlife can seem daunting, especially if you don't feel like going back to school or going through a lot of training. However, according to experts, there are a number of jobs you can begin at age 40 that don't require an immense amount of preparation or new experience. In fact, for many of these jobs, you can often just parlay the skills you've already gained into a new venture. Marketing One of the most satisfying careers for a mid-life worker to consider is marketing, says Travis Lindemoen, managing director of Nexus IT Group, an IT staffing agency. "This is a career option worth considering if you appreciate being creative, working with inventive teams, and understanding what makes people tick. Over the last five years, the av...