benjamingig: got it in one! insure (technically, assure) early, make sure that the assurer has limited scope to wriggle as you get on a bit and don't switch. In some cases, it's one of the few things worth over providing at 21 and having it "just in case" and assigning it as required in later life.
One thing explains why costs increase with age, well two really. Assurance is about paying out about an assured event - you will die eventually. Car insurance, by comparison, is about something paying out for something that may never happen (respectably gambling). Also, unless the stats have changed dramatically recently, the "100 man story" is pretty much a truism, and it's about paying out in every case.
The first part of that story says that of every 100 school leavers aged 16, 25 will have died before retirement. It stands to reason that if you're half way or more to retirement and still living, you've statistically more chance of dieing than your younger mates. Add a chronic disease, and and you'll send underwriters scurrying for cover faster than Jacko's doctor...
thirsty: furrynuff; you probably know all this!.