Decided to run the Marathon

So here’s the thing. I’m 29 years old; no spring-chicken by any stretch of the imagination, but young all the same. And I’ve decided to attempt next years Mumbai Marathon. For a guy who’s not been in peak fitness for quite a few years now, this will take some doing. Besides, I’ve got a crook left knee ligament, which will mean that I will have to be extra careful in training. After all, I can right now only imagine the pounding that my knee will take, first in training and then to run 42.195km. But my mind is made us. Of course, it really is a question of mind over matter.
Oh, and the second part of this decision is to attempt the run in under 4 hrs, which would mean an average speed of not less that 10.6km per hr. That in itself is daunting. My current comfortable jogging speed is around 8.5km/h.
So let’s begin with a few basic parameters:
Age: 29 years and 223 days
Weight: 87kgs (it was close to 98 a few months ago, so don’t scoff at the 87)
Current comfortable jogging distance: 3km
Current Speed: 8.5km/h
Doesn’t look promising, but what the heck.