The reason the Palestinians don't have elections is that Hamas would get voted for again. It enjoys popular support. This 18 year ago and half the population thing is bullshit. Half the population doesn't get to vote anyways when half the population is under 18. That's how democracy works.
On the Israeli side the reason Netanyahu and most Israelis object to a Palestinian state is that it's clearly just going to become a base for launching attacks on Israel, just like Gaza. Palestinians don't want a two state solution, they want to destroy Israel. They say it explicitly in every survey. Go watch videos on YouTube of Palestinians in the west bank interviewed about this question prior to Oct 7th.