"Well, the worst part of being old is rememberin' when you was young."

In the movie "The Straight Story", when Alvin Straight (played by Richard Farnsworth), who had bad eyesight and walked with a cane, was asked, while sitting around a crackling campfire, "So, uh, what's the worst part about being old, Alvin?", he replied,

From Leonard Cohen's song "Did I Ever Love You" from his 2014 album "Popular Problems":

"Was it ever settled?
Was it ever over?
And is it still raining
Back in November?

The lemon trees blossom,
the almond trees wither.
It's spring and it's summer,
then it's winter forever."

Ser Davos Seaworth (played by Liam Cunningham) in season 7, episode 5 ("Eastwatch") of "Game Of Thrones", reminding the younger men that he is old and has seen some shit:

"Nothing fucks you harder than time."

Princess Alice (played by Jane Lapotaire) in season 3 of "The Crown", speaking with Lord Mountbatten:

"There came a moment, around the time I turned 70, when it dawned on me that I was no longer a participant, rather a spectator...."

Neil Diamond - Done Too Soon

...And each one there has one thing shared;
they have sweated beneath the same sun,
looked up in wonder at the same moon,
and wept when it was all done
for being done too soon.

Simon and Garfunkel - Bookends

Time it was,
And what a time it was
It was . . .
A time of innocence
A time of confidences.

Long ago . . . it must be . . .
I have a photograph.
Preserve your memories
They’re all that’s left you.