If you are using default world generator settings, typically Pocket, Smaller, and Small worlds will see Megabeast dying out around 100-150 years. Sometimes a couple survive and in Pocket Mode of course they can sometimes trigger the Age of 'Megabeast'. Medium and Large worlds will typically have Megabeasts surviving for a good while, even well into 1050 years.
Longer History worlds contribute to there being more Bandits and more experienced Bandits, more Towers, more Tombs, and what not. It also gives the in-game deities more time to curse Goblins, Dwarves, Elves, and Humans to become Vampires or Night Creatures, and by that also allow Vampires to form Cults or even take over Civilizations.
Number of Civilizations and Number of Sites are also important for effecting the amount of Civilizations available and sites for Hamlets, Towns, Fortresses; etc, but it also allows for more Historical Figures and and more populated world.
Generally I make worlds I plan to adventure in with-
Small Size: 125 Year History, Very High Civilization, Very High Number of Sites, Very High Beasts, Very High Savagery, and Frequent Mineral Occurrence.
or Medium Size: 250 Year History, High Civilization, Very High Number of Sites, Very High Beasts, Very High Savagery, and Frequent Mineral Occurrence.
I would prefer worlds with Very High Civilizations in Medium Sized worlds but I tend to get a lot of rejects in the default world generator when I try to make those worlds. Sometimes I make Medium Worlds with Longer Histories.