As singer Billy Joel once famously said, “The good old days weren’t always good.” Yet, when we seem to think about the best years of our lives, we tend to think of our past, and primarily in the years of our youth. Scientists have noted that this phenomenon is known as the reminiscence bump, and it’s caused many of us to think that America’s best years just happened to fall in our teenage years. It’s also quite disproportionate among Americans, and depends almost solely on your age.

Previous studies have asked people to name movies and songs that first came to mind, and found that most came from when the person was aged between 15 and 25 years old, no matter how old they currently were. We tend to remember things quite fondly during these years because these are the years when your brain is really starting to develop, and these first permanent memories can be a sort of a “building block” in terms of overall memory.

As you get older, you start to develop fewer new memories, with a large drop coming when you reach your 50s. Your memories gradually start to increase at around three years old, with the biggest bump coming in your teenage years until you turn 40 years old. During this span, scientists say that you retain “a disproportionate number of autobiographical memories” that might allow you to remember what you were wearing to a high school party, but not what your boss told you at work last week if you’re over 30.

“Such events received increased encoding and retention because they are involved in solving basic life issues, are more central to related networks of events and have their availability maintained through increased rehearsal,” the study said. The reminiscence bump “is heavily influenced by the cultural life script – that is, shared expectations about the order and timing of life events in an ordinary life course.”

For this reason, a new study asked Americans to recall when they thought America was at its “greatest,” spawned by Donald Trump’s presidential campaign slogan “Make America Great Again.” The answers spanned over 70 years, with younger participants saying that the greatest days of the United States came very recently. While age shouldn’t necessarily affect when the greatest events happen to you personally, the ones that happen between the ages of 15 to 25 tend to be the most fond in the memories.

In Maryanne Garry’s recent study, she asked 100 United States residents to name off events that they believe established the country’s identity. From the answers that were given, a list of the most common answers was produced. With the top 10 answers in hand, a new group of nearly 500 people were asked to give a particular year in which the United States was at its greatest. The years were then compared to the most common list of events, and under 40 percent of people picked a year that had one of the events from the list.

A majority of the people in the study picked a year that happened to be from their youth, with around 60 percent of people choosing a year that happened before they turned 20 years old. Only a handful of people chose a year that happened a century before their birth, and those over 30 years old rarely picked a year that happened after their 30th birthday. Garry said that people tend to think that “I have a vast soup of experiences in my life – how do I wade through to try and find the most important ones?”

She also says that terms such as “Make America Great Again” have a lot of support because they can be very vague. There isn’t a specific time that people can agree that the country was “great,” but many tend to think that greatness was in the past, rather than the future. “They’re really effective messages” Garry said. “We think we are on the same page, but we are actually on separate pages.”

So whether you think the United States was at its greatest during the end of World War II or when Barack Obama was elected president, it could really depend on your age. Because of the events that happen to us that we hold as culturally relevant such as graduation or getting married, these tend to happen before you turn 30 years old. Reaching the goals almost certainly coincides with major events that happen in the United States, which is why you remember those most vividly and might have a different perception than someone that’s older or younger.