Opinion, only, but for my money there are three guys that sound almost identical to their "heyday", and since one of them has a "heyday" that is almost ten years before the other two, well...
Steven Tyler
Gene Simmons
Paul McCartney
Billy Joel might be on the list, but since he hasn't put out anything fresh since 1876 I can't tell if it is really that his voice is the same or it's just the way he sounds live (he's always been a little rougher live even back in the day).
I know, I know, no one will ever accuse Gene of being a "singer", but I like his voice, and when he sings "Deuce" live, well, it sounds like 1974.
As for McCartney, his set at the Wachovia Center in Philly in '08 (I think) was, to this guy who has seen over 400 concerts in his day, possibly the single greatest vocal performance I've ever seen. Not only did he do "Helter Skelter" 2.5 hours into the set, it was about the 30th song, it was immediately after a performance of "Yesterday" that made me cry, literally, and immediately before eight more of some of the most iconic music ever created. Almost 40 songs in over three hours, and he sang 'em all. No John to help, no George, and no Ringo.