Trump's specific faults are irrelevant to the calculation insofar as they are profound, and they are legion. Anyone who doesn't understand that he should never hold the reigns of power is damn near irredeemably ignorant/hopelessly deluded. Ideally he would keel over and land in a trash compactor.
The 2 year age gap between the two is hardly the point. If that's what you think those calling for Biden to step aside are focusing on you're not understanding what the issue actually is.
I can only speak for myself. The reason I think Biden should drop out is because I. DON'T. THINK. HE. CAN. WIN. If we need to discuss whether Biden's downfall is fair, unfounded because of x, y, or z, the product of unscrupulous conjecture, etc., etc., ok. Ultimately it hardly matters if in the end the remaining conclusion is still that I. DON'T. THINK. HE. CAN. WIN. Biden is infinitely more desirable than Trump, but if he can't pull off a victory it's more important to remedy that than barrel forward into calamity because "I thought it was clear he was going to be the nominee".
Genuinely, I don't know that I could take another Trump term, let alone the prospect of this looming fascism taking root. I would rather roll the dice than play a hand that I absolutely believe will lose.
We can disagree on this. This is a complex situation, and the stakes are high. I'm not going to pretend that I can see into the future. Whatever happens I'm hoping for the best.