Like 173north said, sometimes if you send the serial number to the company, they can tell you the year of manufacture, though some of them only have records from so far back.
All I really know about aging Stübben saddles if that I was told at one point that saddles made in or after 1985 have the blue nail heads, while the pre-1985 ones have regular silver ones, and also that Stübben quit making saddles with suede knee rolls in 1994, though I’m not sure if this information is helpful for this saddle. Some serial numbers start or end with the last two digits of the year of manufacture, but IIRC, I don’t believe Stübben numbers their saddles that way.