I've just done my second half and multiple 10ks. I am 52 and not exactly skinny . Until recently I never even considered running 26 miles but I it is starting to appeal despite my best efforts to suppress the idea!
How much of an increase in time/effort will it be? Bearing in mind I work full-time and have three kids and elderly parents to keep an eye on. I know two women who are running the London Marathon this year who were running halfs last year - but they are both younger and without families.