Not strictly true. You can defer it once for a year, but you have to do it 12 months later. As I said, above, they excused me when I spoke to them - they didn't ask for a medical certificate, which surprised me, but I could have got one if needed.
I was requested to do service at Hove in Dec 11, but I deferred it for a year. When they came back to me last Nov to report to Hove early Dec, I talked to them and got excused on health grounds.
Oh, and I'm just 50, that was the first time I'd been asked.