Is there an agreed on size for Microgames?
This is the crux of the question. There isn't a standard. People unaware of the history of Metagaming and Steve Jackson Games (from another answer to this question) might only consider games like **Love Letter* - with 20 cards and 13 small cubes - to be microgames.
Then Coin Age, with just one card and a few coins, came out (and won a Golden Geek award), further shrinking the component count.
I've been party to "microgame design" competitions where the organizers specify component count (e.g. the 18 card microgame contests on BGG) or a box size (e.g. in-person competitions at conventions, usually sponsored by a publisher with standard box sizes for their games).
So there is no answer. "microgame" isn't a well-defined term. I would suggest that you research the meaning of the term from the context where you found it... since obviously you saw it somewhere and it means enough to you to ask!