Regarding Palpatine looking ‘older’ in AOTC, but then looking a little younger in ROTS, even though it is just because Lucas changed his mind I do have a head-canon explanation for it.

As some theories and fan edits have gone with, I like to think that Sidious’ deformed look is his true face, and ‘Palpatine’ is just a mask he wears, an illusion that takes great concentration with the dark side.

Once Palpatine became Chancellor, I believe the dark side began corrupting him more quickly. But the Sith can feed off of the fear, anger and suffering in the galaxy, giving them more power. Hiding his identity in plain sight from the Jedi while he sat in the highest seat in the Republic took immense focus, and this was even more difficult to do in an era of relative peace. But, when Separatist seceded from the Republic and the Clone Wars broke out, Sidious was able to feed off the suffering in the galaxy it created. This is why Palpatine seems almost healthier in ROTS, after three years of galactic warfare, compared to how he looked in AOTC, before the war began.

I don’t know how long Sidious’ true face was his ‘deformed’ face, but regardless of that, he disposed of his Palpatine mask to manipulate Anakin and the Senate to think he was scarred by the Jedi, and after the Jedi purge he no longer needed to expend the energy to keep up that charade.

This ‘feeding off fear’ idea sort of lends itself to how the Empire operated as well. Even though certain elements of the Empire seemed impractical or inefficient, I think the Emperor saw the Empire as a factory of fear. A machine that created suffering in the galaxy that Sidious could feed on in order to grow in power.

It’s definitely a hand-wavy excuse, and I think I would’ve preferred if he had just became more deformed over the films, but this explanation works for me too.