Other than us as individuals wanting to live long and see our family grow or to explore the wonders of the world. Why does one person living long have more value over someone having a good quality life?

People living longer is generally a proxy for people being healthier. A healthier society is more prosperous since people can work more and produce better output.

Sure but you end up with wealth hoarding as older people live into retirement and by the time they pass on their kids are entering retirement.

Then tax them or otherwise increase the distribution of wealth. "Kill them since it's easier" is such an odd way to look at things to me.

Not sure where I said I said kill them or implied killing them.

I don't see how these are mutually exclusive.