Definitely no limitation on the size, or age, you could draw an entire planet with just one ancient continent, or a harsh, fragmented world during an ice age, or even just a small, primitive settlement of some nomadic tribe of hunters.
The goal would be to make it look wild and yet unconquered by humans. The only age limitation is that life has to exist.
This idea was inspired by an article I read about how cartographers used to fill their map with strange, unknown creatures, and sometimes completely made up detail, something that the article called "horror vacui" - fear of empty space. Those old maps are always so fun for the eye to explore. It's like a mini journey. And there always be "dragons" in the sea.
Well, it's probably just whales, but back in the day people had no means to study ocean and its mysterious creatures.
So, what land would have the most mysterious, awesome creatures, than prehistoric land?