I saw him in Melbourne last year and I thought he sounded fine.
Dont make judgments based on listening to Youtube clips because it doesnt sound great on there - not much does.
Live is different though.
His upper register is slightly strained as you would expect at his age (start of Maybe I'm Amazed etc) but his falsetto was still good and his lower register or rock voice is sensational (in Helter Skelter etc).
Over 3 hours without a drink at his age is still pretty good...
Most of us at 76 will probably be sitting in a corner shitting ourselves so lets keep all this stuff about his voice in perspective.