Instagram has always allowed you to add previously-taken pictures and videos to your Story, but the app imposed one limitation - the media had to be less than 24 hours old. I honestly never noticed that, but it seems silly. Instagram now seems to think so too, and has removed that limit from the mobile apps.
I took that picture of the moon myself! (but not on the phone)
When you add a picture or video to your Story more than 24 hours old, a new date sticker will automatically appear to give the media context. It works just like every other sticker, so you can move it around, resize it, or delete it.
This change is included in Instagram 22 for Android, which you can download from the Play Store below, or from APKMirror.
- Instagram Blog