Studies have shown that reaction time drops about 1 percent per year after the age of 24, but from what I know, the jury is still out on whether the decreased reaction times is primarily a result of aging or a combined result of aging and not consistently engaging in activities that challenge your reaction times, like sports, gaming, etc. A kid aged 16-22 will likely be active in sports and have the luxury to game everyday for at least couple of hours. A 35 year old with a career, family, etc obviously doesn't get to exercise his reaction times and hand-eye coordination as much, so it obviously atrophies over time.
Of course age plays a role, but how much? Roger Federer, at 36, is still dominating a sport that's centered around reaction time and hand-eye coordination, so I think the average mid-30 year old can probably hang with the kids online if he played/practiced enough. The fighting game legend Daigo is 36 and is still a top 5 player in the world, for instance.