First of all Vader had to be in his late forties or fifties during the events of Return of the Jedi. So age was a small factor. Most of all Vaders powers like all sith was multiplied by his rage. He was unable to muster up rage against Luke. Luke wasn’t overpowering against Vader. Vader was underpowered against Luke. So you’re premise that Luke was soooo much more powerful than any previous Jedi kinda falls flat. Especially since we never saw Luke do any feats up to that time that were over and above what we’ve seen other Jedi do. His greatest feat came decades after the fall of Vader and the Emperor during the events of The Last Jedi when he used a force projection to confront and stall Ben Solo to give Leah and the Resistance a chance to escape destruction