I am a VMI graduate and this plate is entirely different to what I wore in the 1970's; ditto for my son who graduated in 2010. The patina on the plate suggests to me that it's early to mid 1900's, esp. the very shiny back. The design is very similar to that used on VA buttons prior to the Civil War, but I'm not suggesting this is remotely that old; not by a long shot. Back then they used an Engineer Castle on their shakos with a VA state seal above the castle. That device continued to be used in the very early1900's, so I'm guessing this shako plate is post WW-1 but not by alot.
The seal design on this plate is the Virginia female armored warrior standing over a slain King, with the motto "Sic Semper Tyrannis" on the sides of the standing figure. These words should sound familiar; they were screamed by John Wilkes Booth when he landed on the theater stage right after killing Abe Lincoln.
Your VMI son or daughter will enjoy this collectible. If anyone knows the exact date of this shako plate, let me know and I'll update my listing.