Before the year 1660, the English government (like a big group of grown-ups who make rules and decisions for the country) had a thing called Parliament. This was a place where important people gathered to talk about laws and make decisions that affected everyone in England.
Now, the thing about these Parliaments is that they didn't always last the same amount of time. Sometimes they would only be around for a few months, and sometimes they would go on for years and years. It was kind of like a game of musical chairs – whenever the people in charge thought it was time for a new Parliament, they would call for an election and choose a whole new group of important people to sit in those chairs.
Sometimes, when the people in charge didn't like what the Parliament was doing, they would end it early and call for a new one. And sometimes the Parliament would get so fed up with the people in charge that they would just dissolve themselves and call for a new election.
So, to sum it all up, the duration of English Parliaments before 1660 was pretty unpredictable. They could last a few months or a few years, and sometimes they would end early if people didn't like what was happening. It was kind of like a big game of musical chairs where the rules could change at any moment!