Busting out the hammer for early retirement

We would like to retire early. Somewhere around the age of 55 or 56. Of course, who wouldn’t want to retire early, right? But we’re in a unique position. My husband has a pre-existing condition that brought about the need for a kidney transplant at the age of 25, just a month and a half after our wedding. We figure he’ll require another transplant in the next 10 years or so, and feel it is absolutely crucial that he gets to experience retirement while he is still healthy.