One person I know who retired early (and loves it) had the following advice. You know the amount of things you do at the weekend? Well, what if you had another five days a week to do them in? Would you be happy or bored?
Currently, at 51, I am actively putting a lot more arrows in my quiver, both hobbies and income generating ability, that if early retirement becomes an option, I will be in a place to choose it if I wish, and still have a lot of hobbies etc. to keep me occupied, as well as non-full time activities to generate supplementary income.
As Bronte said, it is a big step, and you could live for another 30 or 40 years. But luckily there are a large number of ways to approach it, between part time/voluntary work/holidays/paid part time work/hobbies etc.
Also having no children or debts (mortgage will be paid off) helps.