Test your working memory on the BBC website here and contribute to psychological research. James Brockmole and Robert Logie (2013) analysed some of the data collected on the website to report on visual working memory. In this study they analysed the results from 56,000 people aged between 8 and 75. They found that visual working memory increases from the age of 8 until you reach 20 and from then on it declines. By age 55 visual working memory is poorer than it was in an 8 year old.
Try testing your own visual memory, and consider the validity of the research data. There might be other reasons why 20 year olds came out best – not just their superior visual working memory.