Interesting! I think you are probably right. Oddly, under the present circumstances, it is likely to be easier to discover the age of a philosopher after she or he has died than when they were alive and able to be on this panel!
Maybe one of the reasons why *living* philosophers are reluctant to put down their age is professional. In job searches, I believe -but I could be wrong- the person or institute doing the hiring is not allowed to ask for the age of a candidate --just as we are not allowed to inquire into marital status, sexual orientation, physical health. Nor, I think, are we allowed to NOT hire someone because of their age. At least we are not allowed to do so in a direct fashion; at our institution I think we did not hire a candidate who was probably 70 years old on the grounds that the credentials of others were better but also because we judged that the person was not as likely to provide long-term leadership. Age was not THE deciding factor, but I suspect that we did have an *unstated* interest in hiring someone closer in age to our students in order to avoid our department becoming geriatric --I think all of us in the dept were 50 something at the time. Still, maybe philosophers need to be less concerned about age being an impediment either in teaching or doing philosophy. Kant did not publish his first Critique until he was 57 years old, and if the 70 year old was like Kant he might have given us ten awesome years --Kant lived until he was 80.
There might be a related reason why philosophers are reluctant to put down their age or list other personal items: they believe that the validity and cogency of their positions should not be judged in light of their age. Perhaps some philosophers do not want you or I to have "a picture" of who they are, as they think this is irrelevant and distracting. Such philosophers might want you and I to be more interested in what they claim --write or express-- rather than our being interested in *them* as persons.
I wonder whether your judgment of what I have written --helpful? unhelpful? informative? off base?-- would be impacted if you knew my age *which is not on my CV, nor on any public website I know of. Going back to the first point, after I am dead my date of birth will probably be accessible. Most of us who are American philosophers get a short obituary in the American Philosophical Association proceedings. Because that is a rather depressing way to end this post, I end this instead with the following information: I was born on August 25, 1952 in New York City.