i havent run a marathon yet, but plan to next year, at Blackpool or Manchester. I'm not going from 0-26 as i've been running for years, but most of the time for fitness not competition. in 1999 i went from fitness jogging to a half marathon in 6 weeks, and finished in just over 1.30. but whatever you level of fitness, you've given yourself plenty of time to get ready, starting on the run-walk program if you need to, and set yourself goals along the way, such as a 10k race or half marathon.
if you dont get accepted keep on with the training and just do another marathon or half marathon. it may be scary at first, but within, say, two months, you'll be amazed at the progress youve made!
i started running when i was 17 and slightly overweight, and the first couple of weeks were hard, but after that it was fine. you'll start to enjoy it soon, i hope. get some help from your family and friends, get someone to ride a bike with you or run along with you!
best of luck!