Dear Anonymous, Welcome to WikiTree.com and thank you for your question.
As a bit of background, WikiTree.com is a one worldwide family tree. We each add our own branches, twigs and leaves (the leaves are called "profiles") to the same big family tree. The goal is to have one leaf or profile for each person in the world on the WikiTree.
WikiTree is a collaborative family tree, so you can create or edit the profiles here and I can edit the same profiles to improve the information with a biography, pictures, sources and re-sources, and links to other family members with profiles on the WikiTree. These contributions of time, information and attention are donated by the WikiTree members for the benefit of the worldwide genealogy research community.
The profile that you linked to was created three years ago and very little has been done to improve it since that time. It is very likely that the 1509 birthdate was a guess-timate. We are constantly trying to correct and improve the information that we have for all the profiles. Any information that you or your client would like to contribute to this endeavour would be very much appreciated.
Of course, genealogy research is never finished. We need to be constantly vigilant to check and recheck the sources listed on a profile and to look for new sources to add. As Tom said, we value your expertise and hope that you and your client will join our collaborative WikiTree.com community.