The very first people to arrive in Ireland appear to have made it there about 33,000 years ago. This has been dated using archaeological methods because there are no written records that go back to that time. In addition, there appears to be a large cluster of artifacts that date to around 10,000 years ago. While these items have deteriorated significantly over the years, it is clear that people have lived in Ireland for thousands of years, even if their presence isn't considered a part of the greater Irish history. Typically, prehistoric Ireland is considered to start around 4,500 years ago. It is called the Mesolithic or Neolithic age, and is considered to be the start of Irish history.
The first major empire to arrive on the Irish landmass was the Roman Empire. They arrived around the turn of BC to AD, but never took control of what we consider to be Ireland. There was an attempt by the Roman legion to march north to Ireland, but they were too spread out by that time, and they could not take control of the entire area. Instead, they built Hadrian's Wall, which went through England, but did not include a part of Ireland.
Following the fall of the Roman Empire, the Celtic society began to take control of that part of the United Kingdom. At that time, the Celtic society was at war with many of the English kingdoms that were just south of them. In addition, the Irish had to deal with incursions by the Vikings into the Irish mainland. For several hundred years, the Irish had to contend with Vikings stealing their food and burning down their villages. Eventually, the Irish were able to fork alliances between the towns and villages, and they were able to wrestle control of their land away from many of the Nordic tribes that were venturing into the area from Denmark and Norway. While fighting would continue sporadically throughout the Middle Ages, the Irish were in control of their land once again.
No, Ireland is not considered to be a part of England, but Northern Ireland is a part of the UK. This means that Ireland and it's northern counterpart are separate entities. While there have been some movements for greater continuity and greater independence during the past few centuries, Ireland is still an autonomous place. Ireland also has its own cuisine and its own accent. Some people who speak English and travel to Ireland have a hard time understanding the local dialect when they arrive in the country. It is a very popular place for people to visit, and Ireland plays a major role in political affairs that take place within Europe as a whole.
The country of Ireland is 102 years old, founded in the year 1922.