Matter of perspective....
But '73 ammo isn't "old". Not to a collector. To them, old begins before WWII, and goes back from there, generally.
You might think you ammo is elderly, but it isn't, in collector's terms. All it is, is GI surplus ball, with no real value beyond what you can buy new made today.
Shoot it, or keep it (properly kept, it won't spoil). Stored right, it will still be good decades from now.