Here's a listing of support groups in middle Tennessee; if you scroll down, there are a handful listed in Nashville. You might want to call the moderator of each one to see how much emphasis is on Early Onset and what the approximate ages in the group are (for instance, at least one is held at a senior center, which is probably not what you are seeking):
Are you close enough to make Murfreesboro easily? I noticed that one group specifically lists itself for Early Stage:
NHC Murfreesboro 420 N. University Blvd.
3rd Thursday 10:30 a.m.
Tina O'Brien 615-597-6223
And this page of the Alzheimer's Association message boards is specifically for Early Onset people:
And this is the entire under-65 board:
I hope this is of some help to you. Please write back and let us know what you find.