According to the serial # chart in the museum section of this site, it's from 1950-1951. The early post Big B Aristocrats were still top shelf professional horns.
It's from 1950 and looks like a nice one. These are generally referred to as script engraved 156s or series III Aristocrats. My all time favorite Buescher tenor is from 1951 and I've have a bunch of them.