I seriously doubt that. lol Reaction time would have decreased some, sure. But pressing a button fast? Unless you just don't play games alot, I don't think that's possible.
You need to react to know which buttons to press. You don't just continously mash buttons. And reaction time does get slower as you age, so you are at a definite disadvantage the older you are. Experience can compensate for that to a certain degree, but in the end, you still can't react as quick as you used to, and that won't change despite your experience.
There was a comprehensive study done on this where they took both groups, young and old and compared their reflexes. It showed that yes, young players were faster but it also showed that in the end, it didn't give them an advantage because the older players were more experienced. There was literally ZERO advantage. So, it really doesn't matter.
The reflex thing is WAY overblown. If a 40 year old MLB player can hit a 98 mph fast ball from just 60 feet away, I think a 30 year old can play twitch shooters just fine.