People sometimes say that ageing is a privilege that not everyone gets. Woody Allen also said that ageing is better than the alternative. I'm not sure these convey respect but they mean that ageing isn't something to feel bad about. It's a good thing.

"Age before beauty" - when letting an older person sit or enter the room prior to a younger person. "Remember, one day you will be in their shoes"

Yes, there are several idioms that convey the idea that aging is an inevitable part of life and that it is important to respect and value elderly people: "Respect your elders" - This is a common idiom that is often used to remind younger people to show deference and respect to older people. "Age before beauty" - This phrase is typically used in a lighthearted way to allow older people to go ahead of younger people. "You're not getting any younger" - This is a phrase that is often used to remind someone that they are getting older and need to start taking care of themselves. "Time waits for no one" - This idiom conveys the idea that time marches on, regardless of our wishes or desires. "There's no stopping time" - This phrase emphasizes the idea that aging is an inevitable part of life and that we cannot prevent it from happening.

While we have idiomatic expressions that are at least similar or adjacent to the meaning you have in mind, I don't think we have one that is exactly on point.