A long life does not remove the wish to be taken seriously in a present disagreement.

Being argued with properly is a form of respect, and it is often the first thing older people lose. Disagreement gets softened into humoring, opinions are received rather than engaged, and the person on the receiving end notices exactly what happened. A long life does not turn a live objection into a memory to be indulged.

When someone older raises a point you think is wrong, answer it the way you would answer anyone. Say what you think, then let them push back and take the pushing seriously.