Everyone pretty much accepts that age is a factor in sports, mostly due to decreased endurance, slower healing, and the like. I'm not sure if this applies in lower-amplitude types of competition. Bowlers can do well into older age, as can golfers. I can tell you that at 39, my reaction time is still very fast. I'm not as good as I used to be, but this is less a function of my age or coordination, and more a function of not having the time to invest in playing like I used to.
Pinball is perhaps unique in that age does generally predict experience and game knowledge. Escher Lefkoff has amazing raw talent, and has probably played a crapton of games, but it's unlikely he's seen as many games at his age than Keith has in the 30-40 years he's been playing; as such, a player like Keith might have the advantage at an event like Pinburgh, where there is only 1 game in each bank less than 20 years old, and most games coming from the late 70's and early 80's.
I think that if one were to study it closely, I'd wager you'd find that skills don't deteriorate until you develop some degree of cognitive impairment, or you start to have physical limitations that make it difficult to stand. That's why players like Keith Elwin, Trent Augenstein, and Bob Matthews remain competitive despite being in their 40s-60s.
The younger players may seem formidable, because they have more opportunities to play on location than I did, since location play was practically non-existent from my late teens to early thirties. Younger generations also probably benefit from growing up consuming information much more readily that can help play. These kids who have played modern video games have grown up learning complex rules and inputs and have likely had more opportunity to learn how to deconstruct a ruleset and then figure out ways to achieve those goals. After all, Pac-Man was largely about escaping ghosts and eating dots. Sure, there was a pattern to learn, but it was a fairly singular task. A kid who cut their teeth on Metal Gear Solid or Minecraft had to employ a much more complex memory and thought process to succeed. I think that's why there are so many good young players these days.
All in all, I'm not sure anyone will know for sure unless it's studied in a truly academic fashion, but looking at the top 20 in the IFPA rankings, most of the players are older than 35...