I think it's very unfair of @mumsnet not to delete the thread when the OP asked them to
It isn't unfair at all. It's an absolute demonstration of what casual ageism looks like. And the OP has, quite rightly, been pilloried for it.
Interesting how many people have posted stuff like 'lighten up' 'chill' etc - it's exactly what MRA-types say to posters calling out sexism. Surprised no-one has said it's 'just banter' yet. (Although they may have done as I've only skimmed the last few posts)
We can't have MNHQ deleting posts just because OPs don't like the responses that they get. That's not how it works here.