As others mentioned info get out dated and books and websites both are subject to this. Even this site has a lot of outof date info - don't make it bad persay just not the latest. Read as much as you can from as many sources as you can and even ones not exactly about beardies and you'll have more chance at getting a complete picture.
As far as lifespan... remember health and husbandry have a lot to do with it. Genetics plays a role sure, but keep in mind the wide range of care try get. Many dragons on this board suffer from or die from husbandry problems : MBD, gout, obesity, egg binding, infections, impaction, dehydration... Etc. things like MBD are chronic even when the mistakes are fixed and that can have an impact on life span.