It's actually surprisingly close. According to https://en.wikipedia.org/wiki/List_of_Roman_wars_and_battles, there were 21 Roman wars in the 2nd Century BC. US count (https://en.wikipedia.org/wiki/List_of_wars_involving_the_Uni...) for the 20th century AD is 31, but you also have to factor in the fact that the whole world is much more connected, and that the Roman war-and-intervention count was almost certainly limited by communication and transportation abilities of the time. In the context of the ancient world, 21 wars by one state in one century seems like an enormous number. The Achaemenid Persian empire, which existed a few centuries prior and was very expansionist for its time, averaged perhaps 6-8 wars per century, depending on how you quantify wars (https://en.wikipedia.org/wiki/List_of_wars_involving_Iran).