This is rather difficult to answer considering you have not listed any sort of interests or expertise. Additionally the word "fun" is objective. But just to give you an idea of some "fast-track" growing careers, below are just some possible industries you might want to pursue.
Art& Design: You can become a video game designer (salary: $35,000 to $75,000 plus), mobile designer ($52,000), Film a video editor ($50,5000). For more information on these career choices and other suggestions in this field click here:
http://oedb.org/fast-track-careers-art-and-design Communications: You can become a Public Relations Manager ($89,430), Advertising Sales Agent ($43,480), Meeting and Convention Planner ($44,260 to $74,610). For more information on these career choices and other suggestions in this field click here:
http://oedb.org/fast-track-careers-communications Criminal Justice: You can become a Private Investigator ($41,760), Fish and Game Warden ($48,930), Crime Scene Examiner ($47,940). For more information on these career choices and other suggestions in this field click here:
http://oedb.org/fast-track-careers-criminal-justice Science: You can become a Hydrologist ($54,000 to $89,000), Forensics Scientist ($20,000 to $85,000), Environmental Scientist ($65,280). For more information on these career choices and other suggestions in this field click here:
http://oedb.org/fast-track-careers-science Education: You can become a Self Enrichment Teacher ($17 per hour), Special Education Teacher ($50,810), Instructional Coordinator ($56,000). For more information on these career choices and other suggestions in this field click here:
http://oedb.org/fast-track-careers-education