Generally, if your home is original, and built before about 1950, it uses lathe-and-plaster. Between 1950 and 1965, you will find plaster over plaster board, and after that, mostly drywall. BTW - plasterboard panels look like drywall panels, except itís typically a much harder material, end only 2í by 4í
There are other materials or combination of materials you may find in your home, and probably the dates above will vary widely by region, but that will give you a starting point.
Your home was built in 1921, so I would suspect lathe-and-plaster. However, that does not take into consideration additions and remodels. Your best bet would be to cut a hole in the area you are questioning, to see.
Another, maybe less messy way to find out would be to remove door or window trim. Getting behind the walls, like in an attic or crawlspace, may help, but remember, the room may have been remodeled, so there may be drywall panels right over the original plaster.