I came across a personal ad from The Baltimore Sun on August 22, 1890.
In this same cemetery we find a Jacob and Anna Stange. The stones match so I think it's a pretty fair assumption that they were husband and wife. The dates would also fit to be George's parents.
Note that the stones are inscribed in German. This particular church was the big one in the German community in Baltimore. There are a handful of Stanges buried here but I didn't recognize any of the other names. Also it was very common to use the same first names in a family, for example naming your child after your parents.
I believe these could be our ancestors. What I need to find to prove it would be a census record showing George born in 1869 and living with Jacob and Anna, his parents. Or a birth certificate for George. Or some kind of record that can tie them to our Jacob Herman Stange.
Update: I was able to find George on the 1870 census. The last name is spelled Senge. The next page of this record shows a George W Senge born in 1869 in Baltimore, son of Jacob and Anna. That's our family.