Well, all living things on earth have to die, friend - this is not evident of "poor design".
Is a flower, designed poorly? It too, dies. Yet we think it perfect in its beauty and fragrance, its' purpose to bloom, no matter how brief, is proof of its' perfection... but come the long winter - it too must die - this is not proof of poor design, It's only proof of mortality.
Humans too, go through a bloom, it's called puberty and adulthood - and lasts up to approx the age of 40, beyond which it all goes south.
Prepare for your long winter, coz its' coming... GoT fans, this one is specially for you
Peace