In a recent study published on PLOS ONE, researchers discovered through studying StarCraft II players that "declines in cognitive-motor functioning" began past the age of 24. That being the case, there was a decrease in players' speed (measured in the research article with "looking-doing latency") the older they were from 24. Something to consider is that other real-life activities don't necessarily equate speed with efficacy; likewise, a StarCraft II player's skill level did not seem to have a strong correlation with their age.
The research article goes through how older players definitely experienced a decline in their motor skills, but compensated for their loss of speed through more efficient usage of hotkeys, resorting to simpler but equally effective strategies, and focusing more on strategic planning. By delegating more tasks to the user interface, older players could certainly reach similar levels of skills as younger players.
On two measures, older players showed signs of being more advanced than they actually are. Both Unique Hotkeys per game timestamp (more with age; p*<0.001), and Offscreen attacks per game timestamp (more with age; p*<0.001) were strong candidates as compensators. Older players in our sample exhibited more impressive hotkey performance, even when skill was controlled for, suggesting that our participants may be indirectly compensating for declines by offloading demands to the game interface. An increase in attacks to areas outside of the view-screen might reflect heightened awareness of global game information via attention to the ‘mini-map’. Generally then, older players seem better at using available interface features (customizable keys and the ‘mini-map’) than younger players.
The paper is an interesting read if you can make your way through the scientific jargon and number-crunching, so be sure to check it out.
PLOS ONE - Over the Hill at 24: Persistent Age-Related Cognitive-Motor Decline in Reaction Times in an Ecologically Valid Video Game Task Begins in Early Adulthood