At what age do we patronise old people online and not take them seriously?

At what age can an elderly person make a comment, or comments online and not be held to account in relation to the comment?

Is there such an age? Or is it inherently ageist to ignore dumb comments by older people and not respond?

I was recently in an exchange with an older person online and made a comment during that exchange.

Another commenter took me to task and said it was not a nice comment to make to an xx-year-old.

I deleted the comment.

But was I right?

Can older people say what they want and not be challenged on account of their age?

I think, on reflection, that this is an absurd, patronising and ageist position.