The most recent ice accumulation started about 30 million years ago in the Southern Hemisphere. Glaciation in the north started much later.
The last ice age in the history of the Earth includes the Pleistocene and the Holocene. Some researchers put its start at the beginning of the Northern Hemisphere glaciation, 2.6 million years ago.
The climate of the Ice Age was not uniformly cold. It consists of glacial periods lasting about 100,000 years and shorter waves of warming in between, known as interglacial. Even these periods cannot be said to have an even climate. There are warmer periods in the glaciations and colder phases in the warming periods.
Today we are living in a warming period called the Flanders interglacial.