I think I have the solution. I have been stuck at setting my airport, clicking next and seeing my airport from 20,000'. After that, nothing. Now it works. Forget selecting any airport, zoom in on the area you want to start your career and look for little white dots. It seems that these dots indicate the airports that allow Career mode. ONLY these airports. Click on the dot you want and Career mode starts. If you reached a point where you had a beginning of career mode and it subsequently froze I think you hgave ot go back and reset it using the avatar icon on the main page.
Works for me, hope it does for you