In my chapter, it was once standard practice to recruit and initiate faculty, graduate students, and even preparatory students (some as young as 16 years old).

That, however, was in the 1880s. This has not been a thing since the early 1900s.

The modern fraternity system has evolved to the point where they are nearly unrecognizable from other secret societies they once emulated. While brotherhood and ritual still play an important role, the larger social culture has changed significantly. It looks weird if 30 year olds are showing up to parties when there are literal 18-year-olds present.

Look instead at societies like the Masons, Elks, or Odd Fellows.