Posted: Today at 16:59
Depends what you want out of it. If you want to smash a PB then perhaps starting training from a long layoff about 17 weeks before a marathon isn't optimal, but you could certainly train to get round, if that's what you're after.
Also, depends how well your body responds to training, and how injury-proof it is. Sadly, strangers on a web forum can't tell you this, you have to be your own counsel.
If the race allows deferrals close to the race date (6th April I think) then there's no harm in starting to train for it, see how it goes over the next month or so, and re-evaluate then. if you're still way off where you'd expect to be with a couple of months to go until the race, perhaps pick a race later in the spring, or an autumn one. Either way, the sooner you start running regularly, the sooner you'll be race fit.
If you do decide not to run Brighton in April, what will you do right now? By that, I mean, what's your alternative plan for winter running if you don't have a marathon to train for? You could pick a half to train for in spring, or even a couple, or a 10k series, it'll all help in the long term to prepare you for when you do run your next marathon, be that next April or not.