Hmm. I'm of a differing opinion on that. His articles seem to debunk a lot of new ageism and encourage realism in thinking. So he has higher credibility in my eyes. I don't agree though that his indicators of longevity are necessarily accurate. Things like eating a low fat diet are rating high in his scheme, when science is starting to come to a different conclusion on that. So I'd say that while fun, and possibly useful it is based on some assumptions that may be incorrect.
For example I can increase my longevity just by bumping up a rating in whether or not I wear a seatbelt. Given the fact I ride a motorcyle then seatbelt wearing just doesn't apply to my life. One could argue though that I am engaged in a risky activity. But I watched a documentary on quantum psychics that pretty much proved that being engaged in risky versus perceived safe activities have f-all determination on how long you live. Sounds counter-intuitive but in actual fact doing something risky doesn't automatically increase your chances of fatality in life. The relevant skill level of the practitioner changes the equation somewhat.