OK, I'll bite. I have coached 7 different people to marathon OTQ's and here is what advice I have for you.
Motivation:
Yes, this is possible. You are very early on in your running journey and given what you have done in the short time you have been training, I think you probably have the talent to make this a possibility. The key will now be is this something you want enough to do the training and make the commitment necessary to make it a reality.
If the answer to the above is yes, then here are keys I see:
- Consistency: you are early on in your training journey and so will still see good improvements just through consistency and allowing the fitness to build over time. The key to consistency will be getting into a sustainable weekly pattern, no herculean training, just good smart solid repeatable stuff. Biggest error to avoid is trying to do too much or making your increases to big at once. Work hard on your hard days and recover well on your recovery days. Sounds simple but mastering that is the biggest key to success.
- Capacity: obviously with marathon goals then mileage and work capacity will be very important to your success, but its not something you can build up quickly. So just continue to add a little bit each training cycle, but never too much at once. Don't sacrifice your quality work just to get in extra miles. Slowly build up what you can do without sacrificing your quality. Take a longer term approach, so keeping the big picture in sight is important. Don't just focus on trying to get every drop out of the current cycle, but rather letting the current cycle be a solid stepping stone to the next cycle and so on...
- Frequency: you have to do frequently what you want to do well. the body adapts best to what it does most frequently. You are at the mileage level now that your mileage increases going forward will be best accomplished through adding secondary runs. Just 4-5 miles easy runs, added in a couple times a week. Maybe just 2 per week this next cycle, then 3-4 the following cycle, then 5-6 the following cycle. But whatever you do make sure it fits into your work/life schedule and is manageable and sustainable. In your situation (assuming your 70 mile a week is done off of singles), adding frequency will be your key to adding capacity/mileage.
- Mixture: structure your training cycles with a good variety of workouts and paces. Especially in your situation when you are early in running journey and seeing improvements at all distances, then you need to be sure to work all areas - VO2 Max, LT, AT, etc. Structure your training cycles to include a good substantial Fundamental Phase where you work on a good mixture of paces and physiological system. This will be a good opportunity to continue lower your 5k, 10k and half marathon PR's so you are setting HM PR's in your marathons. Getting these times down will help you be more efficient and utilize energy better in the marathon. Then as you get to within the last 8-9 weeks of your marathon go into a marathon Specific Phase, were you focus in more on marathon specific demands, More long tempos, quality added into your long runs, more AT work and marathon pace work. Leverage the gains made in your Fundamental Phase to allow you be more efficient in the Specific Phase.
- Passion: make sure you stay passionate about your running and goals. Never make increases to training load to the point were it robs you of the joy you have for the sport and desire to undertake it. Training should never require a bigger commitment than where running and your gals fit into your life. You should enjoy the journey.
Anyways, those are my thoughts and advice.
Good luck my friend. Dream big, believe in yourself, embrace the challenge and enjoy the journey.