never run a step in life, but wants to train for marathon

Make sure he has good health insurance for the physical therapy he will need in 4 months.

first of all, you have to be strong and patient. You can't just quit after a week. You have to spend months on end of consistent training to even begin to run a marathon. This is the hardest part. Starting and getting into the routine and sticking with it is the hardest part. If you are willing to do that you can do it.

Start slow because injury and setback will be the big risk. Getting overenthusiastic and ramping up too fast with no base will get you hurt.

I would break it up into phases. Pick a 5k in 2 or 3 months and do a couch to 5k sort of plan (walk/run and develop basic fitness). It gives you intermediate goals and will be satisfying to complete. Ease off for a week or two and then start training for a late spring 10k or thereabouts. Then set up a gradual marathon plan starting in summer. Plan to walk/run and just get through the marathon. Worry about time after he has more miles in his legs.

Drinking, if moderate, is not a big deal and will take care of itself if he gets serious. Stopping smoking is important and feeling good from running and having running goals will probably help.

Lots of people troll here, so if you get stupid comments, ignore them. It's a nice goal to want to go from a more sedentary lifestyle to doing a marathon. Quitting smoking is important, as is building the mileage slowly so you don't get injured. Start with some 5ks in the first couple months, then a 10k, and eventually a half before doing the full. Don't be overzealous with your training or you might get injured. Good luck!

The smoking will be a big issue. A pack a day seriously impairs lung capacity. That could mean problems on long runs and workouts that could get serious. It will also mean that training will probably result it respiratory tract illnesses/infections because of the strain on a compromised system.

Booze isn't as much of an issue as long as consumption is moderate. Hard drinking will just mean that morning runs will be crap.

The biggest problem couch to marathoners have is that they do not understand that their bodies are capable of running faster and further than their muscles and soft tissue are able to handle when you first start out. I remember when I first got back into running and did a 5k on a whim. After finishing in @21 min, I could barely walk back to my car and was sooo sore the next day that I couldn't even go for a light jog. So, the focus needs to be soft surfaces, gradual build up of mileage and lots of very easy running. Workouts and long runs should all be moderate efforts, leaving you feeling like you could have done more.

Ever watch "Biggest Loser"?? They take people that are 500 lbs and at the end of the training regime (5 months) they run a full marathon 2 -3 seasons ago one guy ran a 4 hour marathon, not bad at all considering they were HUGE at the beginning. You could definitely do it in a year easily.