Off topic: he's 95 years old?! I don't care how well connected he is, who thought it would be a good idea to have a nonagenarian on the board of a (supposedly) cutting edge health-tech company?!
Such individuals are often chosen to be on the board for their experience and networking prowess.
It's quite true that testing their mental faculty would be a challenge. Therefore the decision could simply lie with other board members based on their observations of his behaviour and the direct contributions he makes to the company.
To suggest that mental acuity is uniformly distributed with respect to age seems a bit "post-truth". The priors at play most definetly suggest much greater scrutiny of a 95 year old, but by no means should they be preclusive.
For the same reason an auto insurance company charges my 86 year old grandmother thousands of dollars per year more than myself; your faculties degrade with age.