Not all Republican candidates or presidents are old. It's just the Democrats. They have this weird, I don't even know what to call it, tradition (?) that everything is done by seniority. Democratic politicians literally wait in line to move up the ladder from local to state to federal government and then the few that are popular enough, become presidential candidates. As you can imagine, this all takes a long time because very few retire from office. The preference to stay in office until death. Like transplant patients, a few die waiting to move up.

This is why the DNC was furious with Obama when he ran against Hillary in 2008. It wasn't his "turn" yet. It was her "turn" to run. And Biden was prevented from running in 2016 because it was still Hillary's "turn" to run. The BS about the death of his son had nothing to do with it. He was told to step aside and allow her to run.

And that's how we ended up with Trump as president! That stupid seniority system. That's why no one will tell Biden not to run. He's the senior politician. If he wants to run, he can and everyone else just has to wait their turn to move up.