Historically, how unusual is it to have a 60+ year period in which no major world powers are at war with each other?

Peace in human history is relatively fleeting.

Before we can discuss periods of peace, we need to discuss what, exactly, a world power is. Because the ability to project force around the entire globe is relatively recent (say within the last 300 or so years), I'll stick to that period. I also don't know squat about say, Ancient China, so I'll just leave that out.

In the last 500 years, since the dawn of the modern age in Europe, there has never been a protracted period of peace longer than about 40 years. This is not to say that individual nation states have not enjoyed longer periods of peace, only to say that a major conflict has broken out among great powers at least that often, but usually much more often. To make things easy, I think a list is in order. Below, I'll recount only relatively large conflicts involving the European Great Powers, until we get to the 19th century, and I'll start including the United States, and then the 20th century, I'll start including China, Japan, and other powers.

The Italian War of 1521-1526 - France, England, Holy Roman Empire
The German Wars of Religion (ended 1555) - This was more akin to a giant civil war, but still.
The French Wars of Religion (ended 1589) - ditto.
The Dutch Revolt against Spain (1566-1648)
The attempted Spanish invasion of England/Spanish Armada (1588)
The Thirty Years' War (1618-1648) - France, Holy Roman Empire, Sweden
The War of Devolution (1667-1668) - France, England, Dutch Republic
Franco-Dutch War (1672-1678)
War of the League of Augsburg (1688-1697) - England, France, HRE
The War of the Spanish Succession (1701-1714) - France, Britain, Austria
War of the Austrian Succession (1740-1748) - France, Britain, Prussia, Austria
Seven Year's War (1756-1763) - same combatants, different teams.
French Revolutionary and Napoleonic Wars (1793-1815)
This is the largest gap
The Crimean War (1853)
Wars of Italian Unification (1859-1871) - saw fighting between France and Austria
Austro-Prussian War (1866-1867)
Franco-Prussian War (1870-1871)
Spanish-American War (1989)
Russo-Japanese War (1905)
The First World War (1914-1918)
The Second World War (1931-1945)
The Korean War (1949-1953) - saw fighting between China and the United States
The Vietnam War (1945-1975) - often considered a proxy war between the US and the USSR
The Soviet War in Afghanistan (1979-1989) - often considered a proxy war between the US and the USSR

Since the fall of the Soviet Union about 25 years ago, there haven't been any major conflicts between great powers, but many of the great powers have been in conflicts with smaller nations. The United States is chief among these Great Powers, having been at war in 1990-1991 (Iraq), 1992-1995 (Somalia), and I'll stop there to avoid hitting our 20 year rule, but suffice it to say, the US has not been at peace for most of the period since then.

EDIT: I should also note that in that largest gap between 1815 and 1853, Europe saw at least two major periods of major instability in 1830 and 1848.