Aonk - Absolutely agree, I have the same issue and (as was a thread on GN some while ago) Statins cause bad wind too.
We don’t know enough about this elderly gent to really discuss this fully yet - Is this a permanent issue that helps relieve him him after a meal? Is it a LEARNED habit from his lifestyle? Has he done this all his life? Is it medical - whatever the answer this man is nearly 90, and in my view is welcome to relieve his wind problem after his meal. It may be offensive and unpleasant to some, but it also may be something he can’t help. Like other posters I would advise asking him why he does it as nicely as poss and if it’s a ‘thing’ of old age, and probably medical, LEAVE him alone!
I’m 76 and have a similar wind issue, I have IBS too, and Asthma which, as a side issue, makes me inhale air whilst I eat.
So I invariably burp after or even during a meal. Luckily I live alone, and mainly eat alone, and it doesn’t happen all the time. In public I try to be circumspect or apologise if a ‘big’ one occurs - but I can’t help it! Have empathy - this might be YIU one day in the not too distant future (Perhaps warn the other guests to ignore?).