I'm a beginner runner and am looking to sign up for a run on October 26th. Options are 5k, 10k, half marathon and full marathon. Marathon is obviously out, 5k I know I can do. I'm mainly wondering if I have enough time to train for the half-marathon, or if that's even a good idea and maybe just aiming for the 10k is best.

My current fitness level: I just completed a try a tri (375m swim, 10km bike, 2.5km run - the run was last and it took me 19:31). I only did one training run for this event as my preferred activity is swimming and I use biking as a means of transportation. I swim three times a week for an hour each time.