State tax filing

Hello, I don't think the reason is age.  the 1099R chart appears ton say only the inherited IRA from spouse ( as surviving spouse) can be excluded.  Since my wife inherited the IRA from her mother,  it is not qualified.  Please confirm.  I know the bottom line is the RMD is subject to Michigan state tax, but I want to make sure of the reason, because if it is age related, at some point it may be qualified as her age changes.  Thank you.