I am thinking of trying a full marathon but I have some major concerns. First of all I'm 51 and have been running 1 1/2 years. I have completed 6 half marathons. My runs are between 4,100 to 7,500 elevation and are in the morning. They have been in Colorado and Utah. The full is in Vegas on November 17th and is an afternoon run, 4:30pm. They have a time limit of 5 hours for the full. I don't think I can finish it in 5 hours. My time in my half have been 2.25 hours. Plus I don't know if I can finish it period!! Should I just sign up for half?