By the time children today are old enough to die from natural causes, we'll have a cure for that.
At some point I think we will 'cure' cellular senescence. Then humans can stay physically in their prime, indefinitely. But there are other limits, like memory. Because memories require physical space, there is only room for a limited amount.
I think we can get past that either naturally, by overwriting old memories, or artificially, by augmenting memory with technology. Research is already looking at brain augmentation with electronics.
So what will be the ultimate limit? Or will humans achieve immortality?
I can just imagine the horrible cancers that would cause, cells that don't die indefinitely producing damaged RNA where essentially only an intense targeted therapy could have an effect.
Or even something as simple as human skin, just if your skin cells didn't die and just kept building up, that would not only fuck up your pores but imagine just having every scar from every little burn or cut you've had in you entire life still visible on your skin.
There could be some pretty horrific Island of Dr. Moreau going on.