The appearance of Jedi spirits has nothing to do with one’s “inner person” as George said of the Hayden change, and in fact Jedi spirits don’t have any objective “true” appearance at all. Instead, they appear to living beings however the living would recognize them. Shaw makes sense as the way Luke imagines his father would look without the scarring, but Hayden would make sense too if Luke had previously seen Clone Wars-era holorecordings of Anakin, such as Artoo might have in his memory banks. Age has nothing to do with it.
In fact, a radically different Sequel Trilogy could have hypothetically cleared this up by giving us a scene of Luke and Rey conversing with Obi-Wan, showing that Rey sees the Jedi General she studied while at the same time Luke sees the Old Ben he knew personally.