Eventually everyone falls off, nobody can get better with age indefinitely and most get worse, although probably most decline due to damage from use and technique problems way before age becomes a serious factor.
Rob Halford has retained a shocking amount of range and tone for his advanced age. I wouldn’t say he’s gotten better but he DID get better with age to a point.
I also thought Bruce Dickinson got a lot better in his 30’s when he left Maiden to do his solo albums. He lost some range compared to his earliest stuff but his tone improved tenfold especially over the stuff he was doing after Seventh Son. He’s only started to sound like he’s losing it after the cancer.
Maximum range is not that important. Tone, phrasing, control and the ability to be consistent are all more important. Unfortunately age will screw everything up eventually. I mean, at some point you’re dead after all.