We all - to a greater or lesser extent - make a difference of some sort by living our lives, which carries on - to a greater or lesser extent - after we are gone.
So, no we are never irrelevant. Inevitably some people are more relevant than others, but we are all relevant nonetheless.
The older we become, the more relevant we are due to life experience, but younger people often don't realise this and ignore older people.
That is their problem (or a problem of modern western culture) but doesn't mean older people are irrelevant.
Yes, indeed our actual lives do have a significant effect.
But, do you know what your great, great, great, great Grandfather did, what his name was, and what he did? Unless you have an ancestor like Winston Churchill, Nelson, Sir David Lloyd George, are mentioned in historical documents, etc, etc, or have paid money to carryout research, like the vast majority of people you do not know. So in modern life, today, as you live, how relevant are those relatives to you?
That is what I meant. Is that not true? It is sad, but a fact, the world and life moves on regardless