Hes old and no matter what you tell him hes scared and will continue being scared.
Exactly what is it you think I am scared of? Dying? People my age and younger die all the time from natural causes. Why would the inevitable scare me?
While I'm not worried about contracting COVID-19, it concerns me that if I caught it, there's a good possibility I would be asymptomatic and not know that I was contagious. In that case, I could pass it on to someone much less healthy than I am which would make me somewhat responsible if they were to get ill and even die as a result.
It's not that I think I am invincible, but the fact remains that I am 75 years old and have never had any strain of the flu. Or, if I did, I definitely never got sick from it.