"A lot of 18-year-olds are like old men. They think they've seen everything"

In this quote, musician Ben Folds is making a contrast between 18-year-olds and old men. He suggests that lots of 18-year-olds have a sense of knowledge and experience beyond their years, comparable to that of an old male. Nevertheless, Folds also implies that this perception might be misdirected, as these young adults may believe they have currently seen and found out whatever there is to understand. This might be seen as a commentary on the arrogance and naivety of youth, as well as the propensity to think we have all the answers at a young age. In general, Folds is highlighting the contrast in between the perceived maturity of 18-year-olds and the reality of their minimal life experience.