Found it on the web and quickly rattled through it. It gave me an age of 38.9 when I'm actually 40.9, so a good result. The thing that stopped it shaving more years off me was because I do NO exercise. Although, I do run a number of jobs, walk a lot and look after two small children, but they didn't have a category for that.
Interesting - so here's the link if anyone else wants to have a go.
http://www.bbc.co.uk/areyouyounger/