Why do Human Beings die?

Why do we have to get old and die .I think the average person lives a thousand(not more then 30,000 btw this isnt accurate number but Im estimating till 80 saying the person is healthy and medical advances of today) .Im 21 now and I feel like my years are mid-way through!I mean 365 days a year isnt alot why couldnt it be 1000 who makes these rules! I think once a person gets old and feeble its like what the point of living .I hate going to retirement homes and seeing old people lie in bed all day.I dont think I want to reach that ever .Also even though they say when we die our kids live through us its still like ok but I myself the person who is typing this the spirit or entity controlling my body isnt going to live on or will I ?.I dont know if reincarnation is true. And what if I dont have kids?You know I may not like some people but I feel like I may miss some of them when their dead.