Yep, agree with everyone else, zero-to-a-marathon is a huge target within a year.

Some people can do it, but i reckon they're very active already - and young (which rules me out). Injuries due to the ramp-up required would be a big reason for it being so difficult.

I usually do at least one half marathon a year, and normally have a long runs of similar sort of length at least once a week for a few months before the event, and i've not yet had the motivation to ramp up to a marathon. It's just SO much further!! (Obviously!!)

Love people with big goals though!

Just get stuck in straight away and give yourself a chance and see how you go.