It really depends on your audience. For most people in the general population, I'd guess that a basic extract class, with some fermentation science thrown it, would be more than enough.
I did laugh at the "senior activity" because 55 is a lot different than 80. I have a friend who brews (he's 68) and won't go to the "silver sneakers" workout group because it's old ladies in chairs, but others his age are "old" in so many ways. I taught him AG brewing a few years ago, and his wife also and she does most of the brewing while he does the heavy lifting.
I'd guess that most people at best have a passing interest. If they are truly wildly interested, then they would already know the basics.
I know that I"m a member of AARP and my husband is going to be 60 in a few weeks, so we'd be in that target age group, more or less, but we'd not even consider going to a class marked "55+" in ANYTHING. I do "regular" yoga and pilates and things, and I'd run from any class considered "55+", so the few classes I've taught (exercise and balance) that were over advertised that age group were more like 75+ in reality.
I guess that is what I'd check- what "55+" really means. Like folks in their mid- late- 50s who are incredibly active, or if this is a class that meets often and they need someone to fill a spot. Next week could be "art", for example.
And I don't think I brew like an old person.