According to this model, the decrease in reaction time from age 20 is probably due to people wanting more certainty before making decisions as they age, visual information taking more time to travel from their eyes to their brain and people taking longer to physically hit the button as they get older.
The analysis suggests that people’s mental speed increases in their 20s, and stays high until age 60. “Until older adulthood, the speed of information processing in the task we studied barely changes,” says von Krause. “People become more cautious in their decisions with increasing age – they try to avoid mistakes. At the same time, the motor processes – the pressing of the response keys in an experiment – slow down with increasing age.”