The most common question I get from people back home is: What's China like? My website: http://www.owendennis.com China blog: http://www.owendennis.com/blo...
Assuming you can run 2 miles now at a nice easy pace (conversational), within 20 weeks you should be able to train up to being able to finish marathon distance at that nice easy pace (between 10 and 12 minute miles) or approximately 4 to 5 hours.
To compete in the London Marathon as a male elite runner you need to be able to run a marathon in under 2 hours 45 minutes (sub 3.15 if you are female). No small feat. But plenty elite runners manage this each year and are in with a shot of claiming victory. The World Marathon Majors compiles the big 5 city marathons (Boston, New York, Chicago, Berlin and our favourite London). In order to qualify you must score in the top 5 in at least 4 of these events. Again, no small feat.