Darkling Elders are described as being fair of look, like a grey skinned elf, and they lack the sunlight sensitivity trait in their stat block.  Am I right then, in believing that the ritual to become an Elder rids the Darkling of the rapid aging?

Less of a rules question, and more of a lore question. The book doesn't say, so your guess is as good as mine.

My guess the aging is just reduced and they have better eyes. Their art work still shows them covering their body with lots of clothes.

This is a great opportunity for you to fill in the blanks with your own lore.