One can consider their age, while also trying to analyze the performance as objective as possible.
Yes, it is definitely impressive that these vocalists in their 70s keep being active.
At the same time, simply listening to what they actually sound like, to recordings and videos, does it actually still sound good? Just because what they do is physically impressive, doesn't mean that some of them are a shadow of their former selves. Take Axl Rose* for a somewhat younger example: does his Mickey Mouse-esque voice nowadays sound good? No, it's silly and absurd. Age has taken its toll, but we are engaging with music with our ears, not with clocks.
* = Kinda bad exampe, he always sucked lol