Old things, antiques, or things that look old. In nature, Sun, moon, trees, even falling leaves are "old"'. Old Roses, too.
For a different spin on this theme, you can make photos in Black and white or sepia treatments that look "Old".
And you can use "Old" photos from your archives.
Post one a day if you can, but not necessary. Please paste a link in this forum so we can take a look.